G-Cans project (Kasukabe)

The G-Cans project (首都圏外郭放水路 Shutoken Gaikaku Housui Ro or Metropolitan Area Outer Underground Discharge Channel) is an underground infrastructure mainly in Saitama, Japan built for preventing overflow of the city's major waterways and rivers during rain and typhoon seasons.

Work on the project started in 1992; it consists of five concrete containment silos with a height of 65 m and a diameter of 32 m, connected by 6.4 km of tunnels, 50 m beneath the surface, as well as a large water tank with a height of 25.4 m, with a length of 177 m, with a width of 78 m, and with 59 massive pillars connected to a number of 10 MW pumps that can pump up to 200 tons of water into the Edogawa River per second.

The G-Cans project is also a tourist attraction, and can be visited for free; however, as the tours are conducted in Japanese, a Japanese speaker must be present in the group to act as a translator for non-Japanese speakers.