A boring machine the length of two football pitches is still under the Channel Tunnel

Named one of the ‘Seven wonders of the modern world’ the ‘Chunnel’ is the one of the longest train tunnels in the world, stretching 31 miles to connect the British Isles with the continent of Europe.

The French and the English dug from each side and met in the middle. When the British finished building their side of the tunnel they decided to leave the digging machine there (after all it had achieved its one purpose). So they drove it off to one side, making a little mini tunnel, and left it there, 250 metres below the sea bed.

https://www.nationalgeographic.org/thisday/may6/chunnel-opens/