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Underground Marvels
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00:01Hidden beneath the city of London.
00:03How is a state-of-the-art energy project powering the financial district?
00:08When we look at the technology now, things have come on a long, long way.
00:12In an ice cave beneath Europe's largest glacier.
00:15They are constantly changing. It's so dramatic.
00:18How do experts study the unstable environment to keep explorers out of harm's way?
00:23The front part of the caves are the most dangerous.
00:26Hidden beneath a rural French village on the front line.
00:30They carved their name to make sure we will remember them.
00:34An underground world fascinates archaeologists.
00:37We are recording this site in order to archive everything.
00:42You can produce a 3D model.
00:44Beneath our feet lie extraordinary chambers, caves, vaults and tunnels.
00:50The span and the size is just crazy.
00:53Some designed and built by humans.
00:56Others formed over thousands of years.
01:00But how were they created and adapted?
01:03By who and why?
01:06You've got to face your fears.
01:08Throughout history, subterranean life has captured our imagination.
01:13We're going further and deeper.
01:15To unearth their mysteries, stories and secrets.
01:27Iceland is an island country, 25 miles south of the Arctic Circle, where the North Atlantic and Arctic Oceans meet.
01:37Home to Europe's largest glacier, this 3,000 square mile mass of ice has created some of the most stunning
01:44subterranean realms on the planet.
01:47We can understand why thousands of people want to come here and see all this.
01:53Why are these otherworldly spaces important to scientific study?
01:58Like you are underneath the sea.
02:00And how are they changing in front of our very eyes?
02:04Glaciers are a very strong force of shaping the Earth.
02:08Even if you visit it tomorrow, it will be a different place.
02:17Iceland covers an area of 40,000 square miles.
02:21More than three quarters of its terrain is uninhabited.
02:24And the island has a sub-Arctic climate of long cold winters and short mild summers.
02:32These are the conditions in which glaciers form.
02:35And beneath them, carved out by streams of meltwater, are some of the most beautiful underground worlds.
02:47Professor Magnus Goodmansen is one of the leading experts in the field of ice caves.
02:53Ice caves are formed in all glaciers with flowing water at the bottom.
02:58The ice tunnels are the pathways of the water that is melted on the surface.
03:03They are formed in summer by the flowing meltwater.
03:09The ice caves tend to be this sort of heavenly blue colors because it's light coming from the sky through
03:17the ice.
03:18Although glaciers can be found on several continents, Iceland is the only place where ice caves are this easily accessible
03:26to adventurers.
03:28And the caves are constantly shifting position and changing size due to the whole mass of ice slowly moving above
03:34and meltwater flowing underneath.
03:38Ice caves can grow to a length of 650 feet.
03:44Because they are always on the move, it is impossible for any visitor to step into the same cave twice.
03:51This is Treasure Island Ice Cave, located 23 feet deep inside a glacier called Vatna Jorkul.
04:02The ice caves can become quite big in a short period of time.
04:08Ice caves that's maybe two meters high may well form in a few days.
04:14Iceland has around 269 named glaciers and Vatna Jorkul is the most impressive, taking up 8% of the country's
04:23land mass, ten times the size of New York City.
04:27A glacier is a body of ice that is large enough and thick enough that it moves under its own
04:33weight.
04:34Glaciers are very active, they shape the Alps and they make the fjords in Norway.
04:40So glaciers are a very strong force of shaping the earth.
04:45At 3,000 square miles, Vatna Jorkul is the biggest glacier in Iceland.
04:51The oldest ice we see in Icelandic glaciers is something like 902,000 years old.
04:57You can see that because there are these really distinct earth bands.
05:01They are ice layers from volcanic eruptions and we have dated these eruptions so we know how old the ice
05:06is.
05:07These layers of ice were formed around 1066 when the world was a very different place and William the Conqueror
05:14had just one control of Britain.
05:17At any given time, each glacier can have as many as 30 ice caves beneath it, but about half of
05:23those will be too unstable for the public to visit.
05:26For centuries, these epic glaciers and the shifting ice caves beneath them have fascinated Icelandic explorers.
05:36Einar Sigurason and five generations of his family have become famous in their homeland, exploring their nation's geology and many
05:44ice formations.
05:46My great-grandfather was in fact the first person to climb the highest peak of Iceland.
05:52Yeah, I guess it runs in my DNA, it's in my blood, you know.
05:58I've been in ice caves for over 25 years.
06:03Just like his ancestors, Einar knows the dangers of ice caves and glaciers.
06:09People have died because of roof collapses when visiting ice caves, so the locals take extreme caution.
06:18Expert guides are a must, with casual tourists being unaware of trapped volcanic gases and steep crevices hidden beneath snow
06:26cover.
06:29Here, when I'm walking across these kind of lowland glaciers, you have plenty of cracks and you see the dangers,
06:37so you can go around them.
06:38But when you are climbing the higher part of the glacier, above 1000 meters, you have much more serious kind
06:44of crevices.
06:45Oh, they get to be 30 meters deep, some of them.
06:48Maybe it's snowing up there, hiding open crevices and you might be going up across soft snow across them and
06:56you could fall through.
07:00For 14 years, Einar has been guiding people around this glacier.
07:06Well, my first ice cave was in my early 20s.
07:10And I still remember it was like coming into a new world I'd never seen before.
07:16And in 2017, he discovered Treasure Island Ice Cave, where water, ice and light combine to create a breathtaking subterranean
07:25environment.
07:28In this particular cave we are in now, you know, you really have so nice details.
07:34To see this material so blue, you know, that's amazing.
07:40There's plenty of light here.
07:42It's probably five meters already thickness of ice here, just above us.
07:47And it's been like you're underneath the sea or something.
07:52We can see inside the ceiling black lines here and there and sand.
07:58The sand that is in there, for example, this is probably many hundreds years old, you know.
08:04So we have history of Iceland here.
08:08These stunning underground spaces constantly evolve with fluctuating seasonal temperatures.
08:14As the warmth of summer arrives, ice turns to water.
08:20It's the heat traveling with the river that kind of melts this into this stormy kind of shape.
08:30And this is just the beginning of the system.
08:33It extends nearly 600 feet back into the glacier.
08:39Iceland is definitely the place for ice cave exploring.
08:42You have so many lowland glaciers here and they are so big and easy to access.
08:53Even so, Iceland's glaciers are retreating due to the rate of summer melt exceeding the rate of winter snowfall.
09:02This in turn adds to the instability of the ice caves.
09:06Scientists are keeping close tabs on the glaciers.
09:09Can technology keep explorers safe from danger and ensure the future of these natural relics?
09:22Iceland's glaciers are natural time capsules, yet they're getting smaller each passing year.
09:28With as many as 1,000 visitors every day between October and March, it's vital to make sure they're safe.
09:35Stefan Mantler from Iceland's search and rescue team monitors the constantly changing Vatnajorkul glacier from above.
09:43When you think about where you enter an ice cave, it is almost always from the front of the glacier,
09:48where the ice is the thinnest and where it is most susceptible to change and to melting the way.
09:53So the front part of the caves and the roofs there are the most dangerous and the ones that we
09:59want to really have a very good eye on.
10:03This is a part of the glacier that we visit very often.
10:05And so even coming here in prior years, we saw a lot of change and I found it important to
10:11try to document these changes.
10:16So to actually map the glacier with the drone, I need to tell the drone to take a lot of
10:22pictures from a lot of different angles.
10:24And then my computer at home combines them essentially to 3D models so we see really also the shape of
10:30the glacier and how that changes.
10:32Standing here on the glacier, it looks very permanent to us, but it really is not. It's almost alive. It
10:37changes every day.
10:39It's important for Stefan to regularly monitor how the glacier and its ice caves are changing.
10:46The glacier we see, it not only moves back from the front, right, it becomes thinner with its entire surface.
10:53And so if you think about caves, for example, ice caves, the roof is only a certain thickness.
10:59And so if the glacier changes, the roof becomes thinner.
11:06Stefan's work with the drone from above means his search and rescue colleague, Sola Sveinbjörnsdotter, can investigate what's going on
11:14below the surface.
11:19There's a lot to think about when you're visiting ice caves like this.
11:23We try to look for things and we have a few red flags, if we can say so, that we're
11:28searching for.
11:29Like, do we have cracks in the ceiling? Is it not touching the ground? Is there a lot of water
11:34in it?
11:34Any weather change, often just from warm to cold, can also make some tension in the ice.
11:40So there are a lot of indicators that you're looking for.
11:43And it's not just one factor that we can just say it's, you know, it's going to collapse if it
11:48goes beyond 10 degrees.
11:50It's not that simple, you know.
11:51Ice caves are alive, that they are constantly changing, evolving.
11:56It's hard to describe to people without seeing it, you know, because it's so dramatic.
12:03Imagine if you visit a place like this, it will never be the same.
12:07Like, even if you just visit it tomorrow, it will be a different place.
12:11And I think that's what makes it one of the most amazing places you can visit.
12:19The entrance to this giant ice cave is accessed via a 23-foot descent down the glacier.
12:27Einar regularly guides groups of tourists through this tricky terrain.
12:31So he meets with Sala to get the latest updates on how these subterranean spaces have changed in the past
12:37few days.
12:38It's changing so fast and so much that you never know what to expect.
12:43You take a picture one time and then you come in a week and it's completely different.
12:47That's the beauty of it, I would say. You know, you're always finding new things and learning.
12:52Always exploring.
12:52I always find, like, in the start of each season, like in September, October, it's like all in treasure hunting.
12:59Despite their popularity, the ice caves may not be here forever.
13:03Since 1995, Iceland's three biggest glaciers have shrunk by more than 55 million cubic gallons.
13:11The equivalent of draining Lake Tahoe one and a half times.
13:16Any acceleration in the glacial retreat could suggest dire consequences on a global level, such as increased extreme weather events
13:25and rising sea levels.
13:31They can disappear very quickly. They are very sensitive to climate.
13:37If things continue as they have with climate change, in 100 years there will be no glaciers and no ice
13:44caves to visit.
13:48It was an ice cave I would go into in the year 2010.
13:53Also another ice cave where the red rocks are.
13:56And since then, now the glacier is like twelve or thirteen hundred meters up there.
14:02It has reseated over one hundred meters per year.
14:04For a thousand years, the Vatnajörgul glacier has been a significant part of Iceland's landscape.
14:13Its people hope to continue exploring this ever-changing subterranean environment for generations to come.
14:21You really have to stay on your toes to enjoy the underground walls of Iceland.
14:35The city of London, also known as the Square Mile, is the centre of British finance and one of the
14:41world's most influential business districts.
14:45Almost half a million people commute into this compact area every weekday.
14:51These workers and their employers have huge energy demands and put a major drain on the power grid.
14:57You wouldn't dream of putting a power station in the middle of a city.
15:00And few realize that an energy source lives directly below the city, within a fascinating network of tunnels and chambers.
15:08Some are centuries old. Others were created during World War II in London's darkest hour.
15:14Under this huge area, it was completely flattened, devastated by the Blitz.
15:20What subterranean structures from the past are shaping the future?
15:24Welcome to the old engine room.
15:27Wow, this space is enormous.
15:29And how can 21st century power be distributed around a complex underground network in a city that never sleeps?
15:36People are totally oblivious to what's beneath their feet.
15:54On the outskirts of London's financial district stands a 19th century building.
15:59It's actually the powerhouse of the city, but it goes largely unnoticed by passers-by.
16:05The street-level facade disguises the vast system of underground spaces, which house the largest urban combined heat and power
16:13system in all of the UK.
16:15At the center of this labyrinth lies an impressive four-story energy station, and John Armstrong is its director of
16:22operations.
16:24When I tell people where I work in London, they don't believe that there's a power station right in the
16:29middle of the city, and it's actually only when they walk past they realize what's here and look in a
16:34bit more detail.
16:36So how did a massive power plant end up in the middle of a century's old district of London?
16:42The historic Smithfield meat market may provide the answer.
16:48London's medieval meat markets date back over 800 years, when cattle were originally driven into a large open space and
16:55sold off.
16:56The markets were then mechanized with the introduction of railways in the 18th century.
17:03Smithfield's open-air market was closed in 1855 and redesigned in 1860, which gave rise to a system of underground
17:11spaces that have been integral to its growth and expansion over the years.
17:19Roger Morgan, an expert in subterranean, has been investigating the legacy of the changing uses underneath these buildings.
17:27We're standing in Smithfields, which is the medieval meat market.
17:32Below the main selling floor was a huge railway goods depot, where the meat trains from the north would discharge
17:43their cargoes and it would be hoisted up onto the selling floor on hydraulic lifts.
17:49And then next door is a coal store for storing the meat, which wasn't sold immediately.
17:54The meat was sold wholesale to London's butcher shops. Huge cold storage units were built in the basements and streets
18:01surrounding the new market buildings.
18:04Meat was kept here deep below street level under temperature controlled conditions.
18:10Carcasses, generally cows from the market over the road, were bought in and kept cold in this building.
18:16This room is 20 metres long, 10 metres high, 10 metres wide, so 2,000 metres cubed.
18:23Potentially you could fit about eight double-decker buses in here.
18:27So this is original steel work holding up the structure from the coal store from 1895.
18:34In the late 19th century, as electricity and refrigeration developed, coal-powered boilers were installed below the cold storage room.
18:42Here they generated much needed power for the Smithfield market.
18:46In this vault over here, this vaulted structure, which is all brick lined, you can see some of that history
18:53from the original coal power station that was here.
18:56And you can actually touch the walls that in 1895 they burnt coal in this space.
19:03It's absolutely amazing to think that over 100 years ago, people doing the same job that I do now were
19:11here very, very differently, but generating power and distributing it around the city.
19:17The market continued to evolve, with enormous underground warehouses lined with carcasses waiting to be sold, and remained busy for
19:26most of the 20th century.
19:28Until World War II, when the city of London was heavily bombed.
19:35With the last of Germany's huge rocket-propelled missiles hitting Smithfield in March 1945, killing 110 people and injuring dozens
19:45more.
19:49London's authorities quickly made plans to rebuild the city, and especially make use of its underground spaces.
19:57Roger is looking at a 1940s map, which shows all the plots ideal for redevelopment.
20:03So in orange is the area devastated by the Blitz and the V1s and the V2s.
20:10The whole area was completely flattened, which gave the opportunity to the City of London to redevelop the area comprehensively
20:19and provide much more service subways.
20:24So nearly every modern building since the 60s in the City of London will have a huge, extensive basement.
20:31So the potential for development for the network in the future is obviously highly significant.
20:39The existence of these post-war spaces, some of them three stories deep, proved to be an asset.
20:47The cold storage beneath Smithfield Market closed its doors as a refrigeration plant in the 1970s, due to advances in
20:54technology.
20:57What would arise in its place would provide a new energy source for the City of London.
21:11Beneath Smithfield Meat Market in London lies an underground world that powers the city.
21:17The former cold storage facilities hidden beneath the streets were repurposed in a phenomenal way.
21:23A power station was built in its place to supply power, heat and cool water for air conditioning.
21:30Known today as the Citigen system, it was powered by two 350-ton ship diesel engines and weaves its way
21:40through the subterranean heart of London's financial district.
21:43The use of existing spaces saved on the cost of digging new tunnels.
21:48Kish Barrett manages this subterranean power network.
21:52You wouldn't dream of putting a power station in the middle of a city.
21:55However, the use of subways and underground locations where people are totally oblivious to what's beneath their feet is a
22:03clever way of delivering local energy.
22:05We could only really do this given the access to subways, tunnels and car park locations.
22:12Otherwise, we would have to be doing civil excavations in major roads.
22:18Nearly four miles of underground heating pipes and nearly three miles of cooling pipes deliver vital energy supplies to various
22:26residential, business and public buildings.
22:29The Citigen underground complex is not open to the public, but Kish is giving Roger access to the heart of
22:36this subterranean network.
22:37I'm interested in getting into the building, which apparently is extraordinary.
22:42Though they never see it, tens of thousands of people above ground benefit from the cutting edge redevelopment of this
22:49former cold storage site.
22:52Welcome now to the old engine room.
22:56Ah, thank you.
22:58Wow, this space is enormous.
23:05So this is where the old engines were sited, and you can see the vastness of the room really gives
23:11you a feel of how big that equipment was.
23:15Is that soot?
23:16It is. It is. It is. It's the exhaust from that engine process.
23:22In 2016, the two 80s era diesel engines were removed to make way for two brand new low emission 4
23:30.3 megawatt natural gas powered engines.
23:34They were so large, the equipment had to be brought down in pieces and reassembled underground.
23:40The upgrade cost 32 and a half million dollars.
23:44These new efficient engines mean that the Citigen complex can now supply tens of thousands of megawatt hours of heat,
23:51electricity and cooled water to more than 11,000 homes and businesses in the city of London.
23:58In no other UK city can a combined heat and power plant be found on this scale.
24:04When we look at the technology now, the higher levels of efficiency, how quiet they run, and also how we
24:12use technology and digitalization, things have come on a long, long way.
24:17This power station is known as a combined cooling heat and power plant, or CHP.
24:23These new natural gas powered engines are 80% more efficient than conventional power stations that burn fossil fuels and
24:31are lower in emissions.
24:33The plant generates enough electricity annually to boil 2 billion cups of coffee, enough cold water to run 42,000
24:41fridges, and enough hot water to fill 70 million baths.
24:45The system has the ability to capture and reuse excess heat at every stage of the energy production process to
24:52keep down fuel use.
24:56It's all monitored from a central control room by Leke Oluwole.
25:01This is central London's biggest tri-generation facility.
25:05Tri-generation is the ability to create heat, chill and electricity from the same source.
25:10Up here, we optimize the production of heat and chill, which ensures that the CHP is more efficient than a
25:16normal gas engine.
25:18We store the excess heat in the thermal stores.
25:21The thermal storage is like a giant central heating hot water tank.
25:26This is where we generally store our production of heat.
25:29It's full of hot water.
25:31The volume of the thermal store is 320 meters cubed.
25:34It takes about two and a half hours to fill it.
25:37This is the beginning of the thermal journey where the hot water from the thermal store goes into the pipe
25:42and then goes onto the network.
25:45Even as the hot water completes a circuit of the network, it remains at a high temperature
25:50because much less energy is needed to bring it back to a boil versus heating it from cold.
25:56The whole tri-power system runs a total of six miles.
26:01Manager Kish and subterranean expert Roger are following the water flow as it winds through and makes clever use of
26:08the existing subterranean spaces.
26:10So Roger, now we're going down into the basement areas of the meat market.
26:14Okay.
26:15We can see where we've used some of the pre-existing space to use for the distribution of the network.
26:21And it's also a car park.
26:22It's now become a car park, refurbished as a car park, but previously it had been used as storage and
26:28also for transporting meat to this location.
26:32We're probably about 250 metres from the power plant.
26:37The pipes are running along the length of the underground car park.
26:41It's this sort of area or opportunity that we look for to get energy from point A to point B,
26:48such that we're not having to do excavations in the road.
26:51Yes, which is an interesting feature of the whole system.
26:55So what we've got here is four sets of pipes.
26:59Two sets are the flow and the return of the heating system, and then there's the flow and the return
27:04of the chill system.
27:05So the whole thing's a bit like a domestic central heating system, only 200 times bigger?
27:10Absolutely, the flow and return.
27:15Exploring this space, I would never know what these pipes are, so it's fascinating to find out.
27:20One of the first beneficiaries of the energy system is the iconic Barbican Estate, rebuilt after the area was bombed
27:28during the Second World War.
27:30It was constructed between the 1960s and 1980s, with a mixed use of private homes and a public arts complex.
27:38Here's the run of the pipes coming through the building.
27:41And again, this is allowing us to use underground space, not only to serve the energy requirements for the Barbican
27:48Air Centre itself, but also take that energy beyond the Barbican Air Centre to other buildings along the network.
27:54The furthest destination on the energy chain is London's Guildhall.
27:59Dating back to the 15th century, it was also badly bombed during World War II, although reconstruction allowed for the
28:07addition of new basement levels, which the water flow now makes use of.
28:13So, we're three storeys down, ten metres, and it's the deepest part of the Guildhall.
28:19Where we were standing was the southern fringe of the Blitz bombing, so to the north of us there was
28:24complete devastation.
28:25There was just rubble at the end of the war, so there was a huge potential for the whole area
28:31to incorporate service subways between all the buildings,
28:35which advantages Citigen now, in that they can now lay their pipes through them.
28:42Even though the energy has flowed through a labyrinth of tunnels, it's clear from the monitors how efficient the tri
28:48-energy system is, right up to the extremities.
28:51Ah, yes. It's showing the temperatures of the water going in and out.
28:57So, the in temperature is 93.7, and the at temperature is 71.3.
29:06So, the water is coming from the hot water store at Citigen, is reduced by 20 degrees and is returned
29:15to Citigen,
29:16and then they only have to boost it by 20 degrees, rather than reheating it from scratch.
29:21The Citigen system has drawn 68 degrees Fahrenheit of energy from the water.
29:27But by sending that heat back into the system, maximum efficiency is maintained.
29:34What's underground, the subway tunnels, the car parks and basements, allows us to install a network in those locations underground
29:43that's benefiting above ground.
29:45As our cities expand, our needs for more efficient energy grows.
29:51Isn't it fantastic that these underground worlds are supplying low carbon power to the city of London's iconic buildings?
30:13Naur is a small village in the Somme Valley, in the Picardie region of northern France.
30:22Just east of the village, on a wooded limestone hill, is a cluster of farm buildings and a small chapel.
30:29They disguise the entrance to a subterranean labyrinth.
30:35For nearly 2,000 years, this tunnel system has played a vital role in the lives of the people of
30:41Naur,
30:42as well as others from around the world.
30:45They were hiding here to escape from the enemy.
30:48Today we know English, Irish, American, Australian, Indian, Canadian, French.
30:56To what extraordinary lengths did the locals go to create a fully functioning underground world?
31:03We can see here traces from smoke, because at that time they didn't have electricity.
31:09And what can state-of-the-art technology reveal about this precious historic time capsule?
31:31Underneath the city of Naur is one of the most captivating subterranean systems in northern Europe.
31:38It runs 72 feet deep and extends for more than a mile.
31:44In all, there are 28 galleries and 300 chambers in this underground complex.
31:50The earliest passages date back to the 2nd century AD, when the Romans dug down into the hill to quarry
31:56limestone.
31:57Caroline Le Bourgeois is in charge of this 2,000-year-old wonder.
32:01When I first came here, I did not expect to discover a place like that.
32:08It was just amazing.
32:12Nearly two kilometers tunnels here, all made by the hand of man.
32:19Nearly 2,000 years since a small Roman quarry first scratched the surface here.
32:24Two miles of tunnels and chambers have expanded this site into an underground world.
32:30But for what purposes? And by whom?
32:35For centuries, this area of northern France and its people were under constant threat from invading armies.
32:42People from the village knew that there were a lot of quarries here in this area.
32:48And they just transformed quarries into those tunnels that force shelter for them.
32:55On the top of our head is just forest.
32:58And thanks to trees, we are protected.
33:02During times of conflict or invasion, they could have found themselves living and working down here for months at a
33:08time.
33:09At that time, there were a lot of invasions in this part of France.
33:14And just to escape from the enemy, they were hiding here themselves in this shelter.
33:22The more the locals sheltered here in the Middle Ages, the more specialized the underground city became.
33:28They constructed wells, stables, bakeries and chapels in this maze of caves and tunnels.
33:36This is the chapel of the underground.
33:38And this is exactly like a real church.
33:41We know that they were here only to protect themselves.
33:46And just taking the time to build the chapel inside this shelter is just, for me, amazing and like crazy.
33:55Villagers living in these underground spaces still had to cook food and stay warm to survive, both which require lighting
34:03fires.
34:04The people who excavated the city beneath Naur came up with an ingenious solution to keep smoke from escaping to
34:11the surface and giving away their location to enemies.
34:16They channeled the smoke through chimneys of existing surface buildings, like a windmill.
34:21On the top of the hill, if they let the smoke out, that was very smart.
34:27We can see here traces from smoke, because at that time they didn't have electricity.
34:34At the height of their use in the Middle Ages, the system of 300 chambers could accommodate almost 3,000
34:41inhabitants.
34:42In the room like this, just imagine that on the floor you have a straw, only straw.
34:48Twelve people could live here, a family.
34:51And all the rooms are different. Each room had his family.
34:55His family has a door, a key for his own room.
35:01In subsequent centuries, the tunnels continued to protect the residents of Naur.
35:07Evidence of their use is still being discovered by researchers.
35:13Gilles Prilot, a historian and archaeologist, has uncovered significant artifacts in these tunnels, dating back to the 17th century.
35:23The first time I entered in this cave, it's for archaeological research.
35:32During my research, I discovered pieces of pottery, coins, musket bullets.
35:39And that proved men was here, occupied this site, during the Thirty Years' War.
35:49The Thirty Years' War raged in Central Europe between 1618 and 1648.
35:56During this period, the French Kingdom fight with the German Kingdom and Spanish.
36:04Begun as a war for religious freedom, it was one of the most destructive conflicts in human history, resulting in
36:118 million fatalities.
36:15Following the Thirty Years' War, this part of Europe gradually became more peaceful and stable.
36:21The tunnels were eventually forgotten, until an amazing rediscovery occurred that continues to this day.
36:35For almost 100 years, the Naur tunnels near Somme, France were largely forgotten.
36:42Then, in the late 19th century, they were rediscovered.
36:46In 1887, the priest Danicourt, the priest of the village, rediscovered the site.
36:55He heard about those tunnels, those undergrounds in the village, and he wanted to rehabilitate the site and to make
37:04the site famous, to present the site to the world.
37:07A passionate archaeology and history supporter, the abbot Ernest Danicourt was determined to revive the forgotten tunnel network of Naur
37:16as a tourist attraction.
37:19When the priest Danicourt discovered the site, it was in this room.
37:25This is the largest of the chambers in the Naur complex, called Le Calvert, named after Mount Cavalry.
37:33You are speechless when you are here, because it's like nearly 30 meters high. You feel just really tiny.
37:42I can understand why he wanted to discover the other parts of the underground. It was the work of his
37:49life.
37:50The tunnels were a popular tourist attraction for the next 25 years, even as World War I got underway.
37:57A surprising number of visits were made by Allied soldiers, seeking respite from the horrors of battle.
38:03I learned that the soldiers, during the Great War, they stay on the front line 50% of their time,
38:11and after they go to the back front to take a break.
38:16The soldiers would travel to Naur to join brave tourists, visiting the underground curiosity near the Western Front.
38:27Many of the soldiers who came to Naur recorded their names and personal details on the tunnel walls.
38:33The underground complex contains one of the highest concentrations of historical graffiti of any World War I site.
38:41Today we know there is 3200 names about the Great War.
38:48English, Irish, American, Australian, Indian, Canadian, French.
38:58Sometimes, I carve their names to make sure we will remember them.
39:05Proof that they are here to fight.
39:09Today, perhaps it's my last day, because tomorrow I will return on the front line.
39:18one of the names gilles found and researched is that of british soldier corporal samuel mikosha
39:24he was on the trenches and the german shells fall a lot of office comrade was wounded and some of
39:36them was covered by the soil with his commanding officers dead corporal mikosha gathered his
39:44surviving comrades they dig out and they save this four soldier samuel mikosha survived the first
39:52world war he was honored for his bravery it's a simple man but a real hero this one-of-a
40:05-kind
40:05graffiti serves as a testament to the experiences of thousands of allied soldiers and makes the
40:11tunnel systems significant to historians over the course of two years a cultural heritage team
40:18spent 20 days scanning now and then building a walkthrough 3d map of the labyrinth to preserve
40:24it for generations to come pierre gruesomeyer is the team leader we are recording this site in order
40:34to to archive everything you can produce a 3d model and after that make some 3d printing or some
40:44replicas the team's efforts to accurately record the tunnel system are due to the site's historical
40:51significance over several centuries we are starting to to scan there with the laser scanner and you may
41:00see all around the side is white spheres each sphere we have very accurate coordinates and that will
41:07help to merge everything together in the best way mapping the extensive network at Naur has been a vast and
41:17painstaking project each of the 300 chambers has intricate details to be digitally recorded dating
41:23back to the site's origins as a roman limestone quarry today we are mapping this underground quarry this underground
41:33quarry is very interesting for us because there is a huge volume we can better see a false and geological
41:39structures
41:43for more than 2 000 years the underground city of Naur has been at the heart of this community
41:50those who look after it today are determined to make sure it remains that way
41:57it's beautiful we have to preserve it we have to continue the work no one else you can find an
42:08underground world like this
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