00:00London's subway tunnels are hotter than the city above, permanently.
00:04The London Underground runs 10 degrees C warmer than street level.
00:08That's not a malfunction. That's just Tuesday.
00:12The Central Line regularly hits 35 dig in summer.
00:16That breaks workplace temperature laws.
00:18Every building above ground must comply.
00:22Underground? Different rules, apparently.
00:25Here's why it can't be fixed.
00:27Victorian tunnels were dug incredibly narrow.
00:30Modern air conditioning units physically don't fit, so the heat just stays.
00:36And it gets stranger.
00:38The clay surrounding these tunnels has been absorbing body heat since 1900.
00:43Over a century of human warmth soaked into the ground.
00:47Geologists say it would take decades of active cooling to reverse it.
00:52The Earth itself has been permanently changed.
00:55Follow for more mind-blowing facts every day.
