That's Tokyo sewers, it's just incredible!
(it's a old series of photo already publish on a lot of blogs and websites)
IMAGES COPYRIGHT 2005 EDOGAWA RIVER OFFICE, ALL RIGHTS RESERVED.
Those following pictures represent the Montsouris underground water tank in Pais 14th district. its the french version of the undergound cathedral.
Those pictures (and more) of the "reservoir Montsouris" are from this very nice site called Exurbis: here