Series following a team of more than 10,000 engineers and construction workers as they race to build a brand new railway under London - Crossrail - London\'s new Underground.

This episode follows engineers building London\'s brand new underground railway, Crossrail, as they take on a Great British obsession - building train tunnels under water.

A team battles to put together the giant jigsaw that will become a cathedral-sized station at Canary Wharf. It\\\'s so big, they have to build it in a dock and underwater. Its architect-designed roof is so complicated it comes in a kit of over 2,500 pieces.