And you thought Tokyo was fantastic on the surface! Just have a look at what’s under your feet: miles of cathedral-like sewers. A neo-gothic labyrinth of engineering wonder! I just wonder if they ever fill all the way up!

I was absolutely wrong about these! This is Kasukabe and a storm drain at that. Still an awesome space though. Here is a press release:

SAITAMA (Kyodo) An underground tunnel built to take in river
water overflow and release it into another river to mitigate flood
damage was shown to the media Monday in Kasukabe, Saitama Prefecture.

The 6.3 km long conduit is 50 meters underground in Kasukabe and connects the Otoshifurutone and Edo rivers.

If the Otoshifurutone River or nearby Naka River flood, excess
water can be channeled into the tunnel from five locations and
temporarily stored in a gigantic reservoir before being pumped up and
released into the Edo River.

The water chamber, dubbed the “underground palace,” features 59
columns, each 25 meters high, that can store 670,000 cu. meters of
water, according to the Land, Infrastructure and Transport Ministry.

The government project began in 1993 with a budget of 240
billion yen, and part of the tunnel became ready for use in 2002. The
system will begin full operation in June.

Historically, the eastern part of Saitama Prefecture has been
prone to floods. The government says the flood-management system will
significantly reduce the danger of floods in the area.