This is so cool (and omg I wouldn’t spend too much time standing in those tunnels):
Fifty metres beneath the teeming megacity of Tokyo is an underworld river system – 6.4km of tunnels, colossal water tanks, massive pillars, giant pumps that remove 200 tonnes of floodwater every second. It’s an engineering marvel built to protect Tokyo against the increasing threat of flooding.
You can download the video here, in case that link breaks later (although then I suppose this link would, too).
(Isn’t it nice how the Australians let the Japanese speak, rather than dub over them?)