首都圏外郭放水路 Metropolitan Area Outer Underground Discharge Channel

World's largest flood control system

This massive underground reservoir completed in 2006 saves Tokyo from inundation by the Tone, Edo, and Ara Rivers. For millennia, the communities depended on these rivers for transportation and fisheries. Later flood control was introduced through levees and dams, and finally, the reservoir known variously as G-Cans and "The Underground Temple" was completed. It's occasionally used as a location for movies because of its impressive interior space. On the Edo riverbank in Kasukabe City is Ryu-Qkan, the pump station above ground with massive drilling blades displayed outside. From December 2021 to the end of January 2022, the facility is inviting the public to tour the cavernous reservoir as part of a tourism campaign.