4m sewers: watch our video of a walk through the Fleet sewer
5-6m cut-and-cover underground: watch our secrets of the Circle Line, District Line, Hammersmith & City Line and Metropolitan Line.
6m Whitehall tunnels: read about our visit to the tunnels beneath the Churchill War Rooms.
15m Greenwich foot tunnel: Wikipedia entry.
19.5m Woolwich foot tunnel: Wikipedia entry.
21m Mail Rail tunnels: watch our video of a ride through the tunnels.
23m Thames Tunnel, built by the Brunels: see our video secrets of the Overground (which uses the Thames Tunnel shown in the graphic)
24m (down to 67m) Tube (deep level): see our secrets of the Underground DVD.
25m (down to 42m) Crossrail: see our video inside Farringdon Crossrail. We also took one of the first rides through a Crossrail tunnel.
30m (down to 66m) Thames Tideway Tunnel: the official page of London's yet-to-be-built super sewer.
35m (down to 60m) London Power Tunnels: the office page for the newly dug tunnels for London's power supply.
36m deep level shelters built during the Second World War: see our recent visit to Clapham Common shelter, which houses a subterranean farm.
40m (down to 65m) water ring main: supplying fresh water to Londoners. Wikipedia page.
55m Shard piles: designer's website.
70m (down to 80m) Lee Tunnel: see our video inside London's deepest tunnel.
Source: HCL FACEBOOK https://www.facebook.com/hydrocleansingltd/photos/a.350911848294660/2275428592509633