Metropolitan Area Outer Underground Discharge Channel

The Metropolitan Area Outer Underground Discharge Channel is the world’s largest water diversion facility, located in the city of Kasukabe in Saitama.
It takes water from rains and typhoons and stores and controls it underground. The water goes through a 6.3-kilometer tunnel, and eventually flows back into the Edogawa River.
Although it is a safety infrastructure, it has been a popular tourist spot. Tours of the facility are available for individuals and for groups. The temple-like architecture of the facility is a popular photo spot. You can see the tanks, but the tunnel is closed to the general public.