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00:01Beneath the surface of our planet lies a vast realm, countless caves, hidden tunnels, and submerged rivers.
00:15On a quest for knowledge, expert cavers descend into an uncharted abyss, where extraordinary discoveries lie waiting.
00:28Armed with the latest scanning technology to penetrate the darkness and turn data into accurate 3D images.
00:44Can a mission into Britain's tallest vertical cave pull off an unprecedented technical feat?
00:51I just looked at that and I couldn't see the top.
00:56To solve a mystery millions of years in the making.
01:02Can divers find the source of a river deep underground?
01:07Yours is the first light ever to illuminate this cavern.
01:11And will decoding these strange cave markings prove the existence of an ancient terror?
01:18People believe that was the lair of the devil.
01:32Deep beneath the British Isles lie some of the world's most hostile caves.
01:42Dark, complex, often flooded spaces that push the limits of the world's toughest cavers.
01:51Caving in Britain is not for the faint hearted. You have to really want to do it.
01:56And one cave has gained a reputation above all others.
02:03The Peak District, known for its limestone and complex cave systems.
02:10The only clue to this cave's existence is a secure and controlled man-made entrance dug into the hillside that
02:19leads into the darkness below.
02:28The exploration team head high into the hills.
02:38The team leader is Dave Nixon, also known as Moose.
02:45We've never had any shelter up here, but it's very exposed. You're about 430 metres above sea level here.
02:52So you get some pretty brutal weather.
02:58Moose was the first person to lay eyes on Titan when he discovered the cave in 1999 by digging through
03:06from below.
03:09But aside from caving lamps, no one has ever seen the chamber in its entirety.
03:19Titan is a vast vertical cave.
03:22It's said to have the longest single drop of any cave in Britain.
03:27But its precise dimensions and volume are still to be determined.
03:37Moose wants to create a three-dimensional scan of the cave to reveal exactly what lies deep inside this hill.
03:46The beauty of a scan is that obviously you'll be able to see the whole thing in 3D in one
03:51go.
03:51Because when you're actually down there, when you're looking, you just see bits of the cave at a time, rather
03:57than all of it.
03:57And you've got to piece it together in your head.
04:02Could the scan data confirm what Moose believes?
04:06That Titan is the tallest cave in Britain?
04:09And can the data also reveal how such a colossal cave was formed?
04:15But creating a precise digital model will require specialist equipment and an expert operator.
04:24Moose has called in one of the world's leading cave surveyors, Ru Walters.
04:30He has used pioneering laser technology to scan nearly 200 caves around the world,
04:36including another giant of the subterranean world, China's Miao Room,
04:41the largest known cavern on Earth.
04:49Titan came into almost folklore in the caving world about 20 odd years ago.
04:55The clue's in the name, it's big.
04:57Bigger vertically than anything I've surveyed before.
05:00So I think that is going to pose us some interesting challenges.
05:03But it should be an absolutely spectacular place.
05:08Hi, Moose.
05:08Good morning, Ru.
05:09How are you doing, mate?
05:10Good to see you. Good to see you.
05:11Very clean.
05:13I'm not going to stay that way for long, am I?
05:15Welcome to Titan.
05:17Shall we get sorted?
05:22Dunk, I'll just clip through my cows.
05:24To size up the challenge facing them, the team want to get their first glimpse of Titan.
05:30Are you ready, Ru?
05:31I'm ready.
05:32Excellent.
05:32Looking forward to it.
05:34One thing's certain, inside Titan, the highly experienced team will need to be secured by ropes at all times.
05:42Very straightforward.
05:43So I'll go down first.
05:45Okay.
05:45I'll give you a hollow from the bottom.
05:47Yep.
05:47And we'll see you down there.
05:48Great.
05:50For years, Titan was only accessible by navigating a labyrinth of caves below.
05:57So Moose got permission to create a faster route in.
06:03He and his friends dug this access tunnel.
06:06A major undertaking that took four years to complete.
06:12The shortcut starts as a narrow 157-foot vertical descent.
06:19Then cuts across horizontally, leading to a small opening into the top of Titan.
06:31All right, Ru.
06:33Yep.
06:33Good.
06:34Ru is about to get his first look into one of Britain's most spectacular caves.
06:42At the end of the tunnel, a small opening offers an overhead view of Titan.
06:47There we go.
06:49Oh, wow.
06:54Caver's lights can only illuminate a small part of this vast chamber.
07:01The rest lies far below, in total darkness.
07:07From the access tunnel, there's a drop through Titan's massive upper cavern to a narrow pinch point called the Event
07:15Horizon.
07:16Below that, there's another steep drop all the way down to the bottom.
07:23It's pretty cool, Moose. It's pretty cool.
07:26When I first looked over the shaft, I really wasn't quite prepared for how big and how deep a hole
07:32it was.
07:32You sort of know it on paper, but nothing quite prepares you for how enormous it is.
07:38OK, how far do you reckon it is to the far side?
07:41Probably about between 80 and 100 metres.
07:45Yeah, she's a big old hole.
07:47Basically, that's what you're going to be scanning.
07:51Titan's vertical chamber is unlike any other Ru has scanned before.
07:57Scanning is a method of capturing objects and situations in three dimensions.
08:04It's only recently, in the last five years or so, that we've been able to apply this 3D technology to
08:10caves.
08:11And what it's beginning to do is allow us to see parts of the cave we've never been able to
08:15see before in forensic detail.
08:17Scans work by sending out pulses of light and measuring the time they take to bounce back.
08:24It does that between three and five hundred thousand times a second all around you.
08:29So it builds up a picture of 3D dots, which represent the object that you're trying to scan in three
08:36dimensions.
08:37To create an accurate record, the scanner needs to be placed in multiple positions around the cave, so the laser
08:45beams can reach every nook and cranny.
08:49But in a giant vertical shaft the size and depth of Titan, there aren't enough flat surfaces to sight the
08:56scanner.
08:57So the question is, can it be done?
09:00I think the best way to scan Titan is to use a different form of scanner that you can use
09:06while you're moving.
09:07So you scan as you move around rather than using static positions.
09:11And then to take that scanner with you and abseil right down the centre of the shaft, scanning as you
09:17go.
09:17But I'm going to have to have a word with the team to work out how we can best affect
09:22that.
09:26Clues to how a massive cave like Titan is formed lie in the limestone that surrounds it.
09:34Analysis of these rocks takes us back to the origins of the British Isles.
09:41Most of the caves that we have actually harks back several hundred million years ago when the UK was in
09:48a different place.
09:53Around 350 million years ago, during the Carboniferous period, the land masses that would form modern Britain lay beneath an
10:02ocean just south of the equator.
10:08Back then we had these tropical seas, full of corals, full of organisms, marine creatures where calcium carbonate was the
10:16body parts that die and form a kind of limey mud.
10:21And that over time will get solidified into limestone.
10:26Gradually, tectonic forces formed the continents, lifting up these ancient seabeds.
10:34Vast belts of limestone cut right across Britain, forming many of its hills and peaks.
10:42This porous stone is instrumental in the creation of caves like Titan.
10:50And so the rainfall that we get here in Britain kind of percolates through that bare rock that moves through
10:56cracks and fractures into the subsurface.
11:00As water seeps into the ground, it absorbs carbon dioxide, creating carbonic acid, which eats away at the limestone, dissolving
11:10it slowly over millions of years, creating complex cave systems.
11:18Subterranean rivers still flow through some cave systems, attracting a different kind of underground explorer.
11:29Cave divers.
11:33Extreme caving at its most demanding and dangerous.
11:41150 miles southwest of Titan, near the Mendip Hills, deep rivers carve their way through limestone rock.
11:51This underworld is known as the birthplace of cave diving, and has been crucial in forging a breed of world
11:59-class underwater explorers.
12:08Wookie Hole is a cave system that snakes through the rock for nearly three miles.
12:14A series of caverns connected by a warren of passages.
12:20In between the dry chambers, some passages are completely submerged.
12:25Flooded caves known as sumps, where only cave divers can pass.
12:33Much of Wookie Hole can only be discovered by the most skilled and intrepid of divers.
12:42Like Martin Farr, a cave diving legend.
12:47He's a veteran with over 50 years of experience of record-breaking underwater cave exploration all over the world.
12:55Cave diving is a totally different ball game to normal caving.
13:02Cave divers like Martin are crucial to the discovery and mapping of Britain's underground rivers.
13:092.40 left, 2.20 right.
13:12See you inside.
13:14We're starting to explore these hidden corners of our world.
13:20Cave divers expand our knowledge.
13:23They chart the sources of springs, streams and rivers.
13:29Uncovering the very start of our planet's plumbing system before water reaches the surface and pours into the ocean.
13:37The science of the subsurface is now a fundamental part of the way that we think of how the planet
13:43works.
13:48Cave diving requires a cool head and nerves of steel.
13:56Today's cave divers use the latest technology, from carbon dioxide scrubbers in their tanks to dive computers.
14:06A far cry from some of the first ever successful cave dives that took place in Wookie Hole in 1935.
14:16They used primitive, bulky dive equipment, heavy brass helmets and clumsy lead boots.
14:24Air was pumped from the surface through long hoses.
14:28The conditions that these pioneer divers had to contend with were pretty, pretty gruesome really.
14:38Despite the difficulties, these pioneers broke new ground.
14:45The 1935 dives began near the cave entrance in Chamber 3.
14:52It took six weeks, but they managed to make their way through 170 feet of submerged tunnels, adding four new
15:00chambers to the map.
15:01Going as far as their early equipment could take them.
15:06Over the next four decades, as technology developed, cave explorers pushed on another 1600 feet, discovering even more chambers.
15:18But there was more to come.
15:24In 1976, Martin Farr expanded the map even further, pushing beyond the 24th chamber into the unknown.
15:34He dived through a new 295 foot stretch of tunnel, and found himself in a new chamber.
15:46When I broke surface, you know, you know yours is the first light ever to illuminate this cavern.
15:53Martin had reached the 25th chamber, a place no human had ever been before.
16:00It is an incredibly rewarding feeling.
16:06You've pushed beyond the limits of any previous explorer, and that is what real cave diving exploration is about.
16:15More recently, other highly experienced cave divers have explored Wookiee to its limit.
16:21The underground river is eventually blocked by boulders 300 feet down.
16:31Wookiee hole is an underworld that has shaped the skills of Britain's best cave divers.
16:39Skills that in 2018, saved lives.
16:47Good evening, 12 children and their football coach, who have been missing for 10 days, have been found alive in
16:53flooded caves.
16:56When the boys and their coach became stranded underground in Thailand, the largest cave rescue in history was mounted.
17:06An international team of cavers and divers came to their aid.
17:12Amongst the rescuers, who were tasked with diving and carrying each buoy through a kilometre of sumps in zero visibility,
17:21were four cave divers, who'd all trained in Wookiee hole.
17:32The rescue was a success.
17:36But it did not come without sacrifice.
17:40Claiming the life of Thai Navy SEAL diver Saman Gunan.
17:54Cave exploration is a dangerous business.
17:58In the Peak District, the team are preparing to scan Titan.
18:04But first, they need to do a test run.
18:09One and a half miles from Titan, lies another famous geological landmark.
18:20Elden Hole is a natural chasm, 200 feet deep.
18:25Open to daylight, it is an ideal place for the team to practice.
18:30Okay guys, this is the scanner.
18:33Yep.
18:34I want to take advantage of this exercise that we're doing here.
18:37Titan is so vertical that Rue has had to rethink how he works.
18:43Scanning from Titan's base would only record a fraction of its towering interior.
18:50Rue's solution is to send the scanner up the full height of Titan.
18:56Ascending by rope and scanning simultaneously.
19:01Something that has never been attempted before.
19:07To achieve this, Rue wants to experiment in Elden Hole with a new piece of kit.
19:13An electric seat.
19:16He hopes it will allow a smooth ascent up the middle of Titan while operating the scanner.
19:24This is one of the highest caves in the Peak District.
19:26But it's also one of the best places to try out this seat.
19:30Obviously it's not as big as Titan, but it'll give you the idea.
19:33And certainly what we're trying to establish today is just the principle of working on the electric power seat.
19:38Absolutely.
19:41Pop it on the edge, I'll step down once.
19:44Designed for use in industrial spaces, the seat will only travel upwards.
19:53It has never been used in a cave environment before.
19:59That should start spinning in a second.
20:03Rue is also testing a new compact laser scanner he's hired for the job.
20:11He will need to operate it while controlling the motorized seat.
20:19Okay.
20:20There's a scanner, Joe.
20:23And then, power on.
20:27And we've got the green light to go.
20:29Lovely.
20:29Okay.
20:30Yep.
20:31Well done.
20:35Is that tight enough for you there?
20:36Just another inch would be lovely.
20:38Another inch would be good.
20:38After securing the scanner, Rue's ready to attempt the 197-foot ascent.
20:45Okay, mate.
20:46Ascending!
20:47Good.
20:55How's the scanner doing, Joe?
20:56Well, it's swinging around a bit now, but it looks pretty good.
21:04A slow, steady ascent is essential for an accurate scan result.
21:12But Titan is much taller, so a swinging rope will be even harder to control.
21:27Together, the seat and scanner weigh about 25 kilos.
21:33Well, you've got a loop.
21:35Yep.
21:36Just so I don't drop it.
21:39And I might need a hand.
21:41Yeah.
21:41Because it's bloody heavy.
21:47Well, that worked a treat.
21:49Was the plan a good one or a bad one?
21:51It's an excellent one.
21:52Good stuff.
21:53We're able to keep a nice, even speed up the pitch with the seat,
21:56and that's going to be perfect for the scan.
21:59The team have come up with a potential method for scanning Titan.
22:04But Titan is more than twice as deep as Eldon Hole.
22:08If they can pull it off, Moose hopes the scan images will help others share in the awe that he
22:15felt when he first set foot inside the cave.
22:25Modern cavers like Moose are the latest in a long line of underground explorers lured by the peaks of Derbyshire.
22:34Rich in lead ore, these hills have been mined since Roman times.
22:42Over the centuries, miners were forced to dig ever deeper to reach the dwindling deposits.
22:50On occasion, they would break through into natural cave systems.
22:56And it was a record of a mining route that led Moose to the discovery of Titan over 200 years
23:02later.
23:04So this document, and all the clues that were in it, were like a eureka moment for me.
23:10And this account was written in 1793, and it was by a chap called James Plumptree, who visited the Peak
23:17District.
23:17And when he visited the Peak District, he visited Speedwell Mine.
23:21Dug in the 18th century, Speedwell Mine is a series of abandoned tunnels which intersect with the natural caves of
23:29the Peak Speedwell Cave System,
23:31a network of passages over 11 miles long.
23:37Plumptree's account described part of the mine system that might give Moose access to undiscovered parts of the Speedwell system.
23:46We just thought, yes, let's go, get the shovel, let's get out there, and let's get on with it, because
23:51we're going to find something.
23:53It was almost certain we were going to find something.
23:56In 1992, Moose and his friends embarked on their epic quest to find new parts of the cave system.
24:04That's what attracts your caver.
24:06Somebody who's into cave exploration, somebody who's got a curious mind, somebody who won't take no for an answer,
24:11is going to say, no, I want to find out what's there.
24:16They struck out into the unknown,
24:19tunnelling through collapsed mineshafts, digging through boulder chokes.
24:24In all, pushing their way through nearly two and a half thousand feet of passage.
24:30Finally, after seven years, on New Year's Day 1999, they hit a small, dark chamber.
24:44Ooh, jeepish creep.
24:49Titan may be big, but the approach to it isn't.
24:58And above here, there's a little antechamber.
25:03It's a Titan.
25:05It was here they realised they were on the brink of something big.
25:10Limestones deposited in beds.
25:12You can see this one's a very dark limestone.
25:15But what you've got here is you've got this, which is a very light grey limestone.
25:22Now I know full well that that limestone there is from a higher bed.
25:26For that rock to have found its way down here, it must have fallen down a cavity.
25:33What kind of space lay above them?
25:36They pushed on up through the rock.
25:40But nothing could prepare them for what they found.
25:44The very last push was a matter of just moving all the debris to the side and wriggling through under
25:49this rock.
25:50Stood up.
25:51I just looked up there.
25:53And I couldn't see the top.
26:01They had emerged into a cathedral-sized space.
26:07A vast cavern.
26:10They had discovered Titan.
26:14We were all absolutely elated.
26:15It was great news.
26:16That moment where you've got nothing stopping you is fabulous.
26:22I personally didn't see it as an obsession.
26:24But in retrospect, I was absolutely driven.
26:28And I was completely obsessed in doing it.
26:31But when you're in that zone, you don't see it.
26:34You don't see it. You just think it as being normal.
26:37But trust me, spending seven years digging a hole in the ground is not normal.
26:44Moose and his friends redrew the map of the Peak Speedwell cave system.
26:49Their final task, creating the shortcut into the top of Titan.
26:55Allowing fellow cavers an easier route in.
27:02While caves like Titan have remained hidden since their creation, there are other caves in Derbyshire that have been known
27:10for thousands of years.
27:13Dark underworlds that became places of deep-rooted terror.
27:2025 miles east of Titan lie a series of caves that harbour the darkest of secrets.
27:33There's evidence here of human cave dwelling dating back 60,000 years.
27:40And something mysterious lurks inside these caves.
27:48Well, caves have always been places that have been seen as mysterious, dark, evil places where demons and devils lived.
27:59So that's why you get all these legends and beliefs about the entrance to caves.
28:04And this is something that seeps into folklore.
28:08That's where evil was found.
28:11Hidden in the darkness is evidence of an ancient fear and dark rituals.
28:21Thousands of enigmatic marks scratched into the walls.
28:31They're found in the darkest recesses of these caves.
28:38Ignored for centuries, they've only recently been recognised for what they are.
28:44So-called, witches' marks.
28:5016th and 17th century protections against evil.
28:56In the 1590s, James VI of Scotland, who had later become James I of England, contributed to these fears.
29:05There was this period when a witchcraft scare was going on.
29:10And the king himself bought into this.
29:12He was out there looking for witches.
29:14He wrote a book called Demonology, which set out how you find witches.
29:19It was a time of superstition, witch hunts, trials and persecution.
29:26During that period, we find a massive concentration, almost on an industrial scale, of people making these protective marks.
29:34But what do these marks actually mean?
29:37You see a certain type of recurring symbol.
29:42The most common example of this is what's known as the Marian Mark.
29:46And these are like crossed Vs, or like an upside-down M.
29:50And they are a reference to the Virgin Mary.
29:55People were using them in a religious context as an evil aversion.
30:00Maybe the cows are not giving milk that particular year.
30:03Maybe people are afflicted by a disease that they don't understand, and they feel the need to make some kind
30:09of magic spell.
30:13This is another interesting one here, which is like an elongated eye with horizontal marks across it.
30:20This is believed to be a representation of the Greek letter for Jesus, Alpha and Omega.
30:29And we also find box-like markings, and these are thought to be spirit traps.
30:36A magic box where it's hoped that a spirit will be trapped, and it will have to go round and
30:42round and round endlessly.
30:44The majority of the marks are clustered in the darkest part of the cave.
30:50A small chamber with a dark hole in the middle.
30:58What was it about this particular spot that frightened people?
31:04You can sort of understand why they would single out this particular part of the cave.
31:08Because when you see it, it does look forbidding.
31:11It's the sort of place that they would imagine the devil and all the various other spirits that they believed
31:16in would live.
31:19This sinister place was known locally as the entrance to hell.
31:26There's a massive drop below me that appears to disappear into the bowels of the earth and into the underworld.
31:32So we've got this amazing density of carvings in this particular part of the cave.
31:37This is where they are really, really concentrated.
31:40And it's clearly because this was seen to be the most dangerous part of the cave complex.
31:45This is where evil was seen to reside.
31:50Anything that emerged into the village environment that was bad, this is where it was traced back to.
31:55So it needed the maximum amount of magical ritual to keep it here, to keep it in its place.
32:09Even to our modern psyche, caves can be threatening.
32:13They conjure claustrophobic nightmares and play tricks on the mind.
32:18It takes a rare breed of explorer to overcome these fears and descend into the darkness.
32:27But for those willing to take on the adventure, the rewards can be spectacular.
32:34Natural beauty formed over the millennia.
32:42One British cave even became the muse of great artists.
32:54It lies on the uninhabited island of Stathar, on the west coast of Scotland.
33:01Fingal's cave is named after a mythical Irish giant.
33:06Its forbidding entrance looms over the surrounding sea.
33:12The astonishing rock formations aren't limestone.
33:16They are ancient volcanic lava that solidified into hexagonal columns.
33:24In the 19th century, this natural wonder drew in visitors.
33:30Poets like Keats and Wordsworth.
33:33The artist, William Turner, painted it.
33:38And in 1829, on a visit, Mendelssohn was inspired to compose his Hebrides overture.
33:47But Fingal's cave hides a phenomenon.
33:52It is fully illuminated by sunlight on only one day a year.
33:59On the 16th of December, the sun penetrates the 225-foot length of the cave.
34:07And bathes its back wall in light.
34:20Sunlight has never entered Titan.
34:23And it's so big, no torch can illuminate it.
34:27Today, the scanning team aim to reveal Titan by using the latest technology to create a detailed digital map.
34:35I'll take that in the scanner and then you take the seat.
34:38Weeks of careful planning have all been leading to this moment.
34:43So I'm fairly confident.
34:45I'm not sure where Roo will be.
34:47I reckon that I'll be a little bit nervous.
34:51Phil, there's quite a lot riding on this.
34:53There's really no reason why it shouldn't work.
34:55But it's new technology.
34:57Joe will operate the scanner inside Titan.
35:00Try and make sure it swings the smallest amount it can.
35:03And I know that's a big, big ask.
35:08In order to scan Titan thoroughly, Joe will attach himself to a rope suspended down the middle of Titan's gigantic
35:15shaft.
35:18Ascending on the electric seat, he'll endeavor to ride smoothly all the way up so the scanner can capture every
35:24rock and crevice in detail.
35:29This can only be done by experienced potholers, experts at caving with ropes.
35:39Even a minor injury underground could result in a long and dangerous rescue operation.
35:44Here are you.
35:47Moose descends into Titan.
35:49His task, to secure Joe and the scanner to the seat.
36:02Joe's going down to do the scan at the bottom of the shaft.
36:07That's going to take him an hour, hour and a half or so.
36:10I'm going down to bring the data out and get it down to the computer to have a look at
36:15it as quickly as we can.
36:19The support team is in position.
36:30Ready to go.
36:32Cable.
36:35This is the moment they have all been waiting for.
36:39OK.
36:40Get it off the floor.
36:42There we go.
36:43There we go.
36:48Turn that.
36:50Lovely.
36:51OK.
36:52Right, stand by.
37:00Joe has lift off, the scanner dangling below him.
37:04Great trip.
37:06Great trip.
37:06Good, mate.
37:07I'll see you at the top.
37:08Yeah.
37:26Joe approaches the narrow lip of the event horizon.
37:50It's very close.
37:53manager.
38:10You can see me.
38:15You can see me.
38:16You know this?
38:20I'm sorry.
38:21I'm sorry.
38:33Finally, Roo goes in.
38:35He has no idea if the scan has been a success.
38:39Is that the precious data?
38:40Yeah.
38:41I'm going to clip it in so I don't drop it.
38:44That's it, I've got it.
38:56I think that went really well, fantastic team effort.
39:00All the data is in here, in the scanner.
39:03It's just a question now of getting it down to the computer, uploading it, and fingers
39:07crossed everything's okay.
39:09You've got some bags in there as well.
39:10Yeah, there's three.
39:16If the team's scan was successful, it will reveal the most detailed images
39:21ever of one of Britain's greatest geological wonders, that has lain hidden in the darkness
39:27for tens of thousands of years.
39:34Now, all they can do is wait for the results.
39:43British caves don't just lure explorers like Moose into their dark underworld.
39:49They also draw scientists and archaeologists searching for evidence of an ancient and vanished
39:56world.
40:00In the Mendip Hills, six miles from Wookie Hole, lies Cheddar Gorge.
40:07It was here in 1903 that workers digging a drainage ditch made a remarkable discovery.
40:15A ten-thousand-year-old fossilised human skeleton.
40:23Cheddar Man is the oldest complete human skeleton ever found in Britain.
40:33His bones, remarkably preserved by the cold, alkaline-rich environment.
40:38Scientists even extracted DNA from his skeleton.
40:43With the skull and DNA analysis, they were able to reconstruct Cheddar Man's face, right
40:50down to the colour of his skin, hair and eyes.
41:10It's not surprising that Cheddar Man was found in a cave.
41:15The earliest humans used caves for shelter and protection.
41:24But cave dwellers, also known as troglodytes, are not just found in prehistory.
41:31There are countless examples throughout the ages.
41:39From the 12th century cliff dwellings of the ancient Anasazi people.
41:45To a Buddhist monastic centre on the ancient Silk Road.
41:54And a spectacular 12th century cave city in Georgia.
42:04Britain has also had its own recent cave dwellers.
42:1015 miles west of Birmingham lies a 250-million-year-old sandstone escarpment.
42:22Here, a series of rock houses was home to generations of inhabitants from at least the 18th century
42:29right up to the 1960s, home to Britain's last troglodytes.
42:36I think to understand the reason why these sorts of dwellings are where they are, we need
42:41to understand a little bit the local geology.
42:45We are sitting on a three-asic sandstone.
42:48Sandstone is a very soft material, therefore it's easy to work, it's easy to quarry.
42:53When the first people came into the area and they noticed these natural features, they
42:58thought, oh, actually, they could be a natural accommodation.
43:03People were drawn to the area during the Industrial Revolution.
43:07An iron foundry opened nearby.
43:10The local economy played an important part.
43:13One of the records is telling us that in 1841, only one dwelling was recorded on this particular
43:19site, with just one family.
43:22By 1851, 1861, we record between 11 and 14 families living on this site.
43:32The homes on display are from the Victorian period, but a more cosy cottage than cave.
43:39Just because these were basic accommodation doesn't mean they were poor accommodation.
43:45All the dwellings had a fireplace to keep warm, you know.
43:48So it was just a very basic way of living.
43:53But times and attitudes changed, and the last family moved out in the 1960s.
43:59People stopped living here mainly for a change in the local economy.
44:03The industrial boom with the iron making has slowly declined, so there wasn't really the need
44:10anymore for these places to be occupied.
44:15The Kinva Edge rock houses offer a window into a unique social history.
44:28Titan is far too inhospitable to ever be called home.
44:32But that didn't stop the expert scanning team attempting to measure its vast interior.
44:38Roo has compiled all the scan data.
44:41Hi Moose.
44:41How are you doing Roo?
44:42I'm well.
44:43The results can now be revealed.
44:45I've been burning the midnight oil a bit.
44:47Hey.
44:47I've put all the data together.
44:49But has all the hard work paid off?
44:52Do you want to have a look?
44:53Yeah, too right I do.
44:54Well, here it is.
44:55Wow.
44:59There she is in all her beauty.
45:01As you can see, we really have captured things very, very well.
45:06That's really good.
45:08No one was certain a vertical cavern of this size could be scanned.
45:13It just depicts the shape beautifully, doesn't it?
45:15Yes, absolutely.
45:17And here it is.
45:19380 million data points come together to recreate an extraordinary virtual underworld.
45:26The first scientifically accurate 3D model of Titan.
45:31Revealing its true shape and dimensions with pinpoint accuracy.
45:38From its high ceiling, through the event horizon, down to the bottom.
45:49The scan reveals Titan's true size.
45:53It measures 476 feet.
45:58It would dwarf the Statue of Liberty with headroom to spare.
46:05Confirming Titan's place in the record books as Britain's tallest natural cavern.
46:14The scan also allows us to zoom in.
46:18To the exact spot where Moose first entered Titan and gazed up into the dark void above
46:27him.
46:28Wow.
46:29Yeah.
46:30Pretty cool, isn't it?
46:31That's like reliving it after 20 years.
46:34So the other thing that really stands out to me is that it shows the geology, it shows
46:39the structure of the cave.
46:41Yes.
46:41It shows how, it's almost how it's formed and why it's there.
46:45The scan reveals the birth of this subterranean giant.
46:51Titan's narrow shape exposes a vertical fault in the rock.
46:55A natural place of weakness that the water exploited as it dissolved the limestone.
47:04But the scan also explains why Titan grew so large.
47:09Amongst the layers of limestone.
47:11A layer of ancient volcanic ash.
47:16So at Titan you've got normal rainfall falling down on a fracture zone where you've developed
47:21a cave.
47:22But the other ingredient looks like this ash.
47:24This is a volcanic ash that was laid down hundreds of millions of years ago.
47:28But actually is very acidic.
47:31So when you get the dissolved water from the rainfall meeting this acid material, it produces
47:37a really aggressive dissolving agent.
47:40Essentially an acid bath that basically bores its way through.
47:44And I suspect that is why Titan is so big.
47:48Over time, this corrosive geological cocktail of water and ash percolated downward.
47:55Anru's scan reveals the enormity of that process.
48:01Measuring Titan's volume proves that this acid water dissolved over 1.5 million cubic feet
48:09of rock.
48:10Leaving behind a 476 foot deep shaft at the edge of the peak speedwell cave system.
48:21It was a giant underworld waiting to be discovered.
48:27So would you say it would be possible somewhere in this country of ours to find something that's
48:31taller?
48:32There's lots and lots of blank areas where there could easily be something else like
48:36that working.
48:37It's postulating it.
48:38That's the easy bit.
48:39Yeah.
48:40The hard bit is finding it.
48:41But that's, I mean that's the whole essence of caving isn't it?
48:43You don't know until you've found it.
48:45Yeah.
48:45That's right.
48:45And that's the thrill of it.
48:47Yeah.
48:47And this is genuine exploration isn't it?
48:49And we're finding new pieces of the planet that we've never seen before.
48:53And it's happening today in Great Britain.
48:57The mission to find the world's hidden caves continues.
49:02Committed explorers like Rue, Moose and cave diver Martin Farr shine light into the darkest
49:10of places.
49:12But one day, their quest could take humanity even further.
49:20In 2009, NASA sent an unmanned satellite to the moon.
49:25It photographed the lunar surface in unprecedented detail and discovered something unexpected.
49:35Caves.
49:38Exploring and mapping these extra planetary underworlds will at first be done by robots,
49:44which are already in development.
49:48I think it's going to create a new explosion of cave exploration on Earth as we road test
49:54a lot of these instruments and start to learn a whole lot about cave systems that we just
49:58can't access here on Earth.
49:59So it's tremendously exciting.
50:02Charting extraterrestrial underworlds is a far cry from the time when caves were our homes.
50:09But as we head towards brave new worlds, they may once again be a haven for future generations
50:15of explorers.
50:19When we think about planetary travel and planetary mission, we're going to have to stay someplace.
50:25And actually, caves are not a bad place.
50:27They protect us from cosmic radiation.
50:30You know, they're having the same ingredients of protection that we had here on Earth.
50:37So caves will probably be a place where we will seek out as places for storage, but also
50:42maybe for residential areas as we start to explore new planetary frontiers.
50:49From our ancient ancestors to the future citizens of space,
50:55mankind's hunger for exploration draws us deeper into hidden realms.
51:01Who will be next to redraw the map of the underworld?
51:13Who are we?
51:14Where do we come from?
51:15Our origins?
51:16Our evolution?
51:17The story of us, more dramatic than we could ever imagine, is revealed through cutting-edge
51:22science.
51:23Human on BBC iPlayer.