The Metropolitan Area Outer Underground Discharge Channel in Kasukabe City, Saitama Prefecture, is the world's largest underground flood water diversion facility, boasting a total length of about 6.3 kilometers. It was built over the course of approximately 13 years, amassing cutting-edge civil engineering technologies. The main role of the discharge tunnel is to, in the case of a flood, redirect excess water from the small and medium sized rivers that flow through the metropolitan area into the larger Edogawa River, reducing the flood.
At the facility, tours are held where participants can observe the underground discharge area at a depth of 50 meters as well as the equipment used. Especially popular is the observation of the giant surge tank that was created in order to weaken the force of the water from the underground tunnels in order to distribute it into the river smoothly. The ceiling of the surge tank is held up by 59 large pillars, and the massive space has the intensity reminiscent of an underground sanctuary. There are three observation courses available, and each one takes visitors to see this underground sanctuary. First is the thrilling Shaft Experience Course, which allows participants to walk along the workers' pathway and take the stairs partway down into a giant pit called Shaft Number One; the Pump Proficiency Course mainly focuses on learning about the pump at the heart of the Metropolitan Area Outer Underground Discharge Channel; and lastly, the Underground Sanctuary Course is a dense, 60-minute tour that includes an observation of the giant pit Shaft Number One. To determine which course you'd like to participate in, please check the official website.
Additionally, at the Ryukyukan Underground Exploration Museum, visitors can go to the Deep Experience Hall and take part in a virtual experience that uses lights, sounds, and videos to recreate the activity of the discharge channel, or see the control facilities through a glass panel at the Operations Room Watching section. There are all sorts of facilities here that endeavor to let visitors have fun while learning about the Metropolitan Area Outer Underground Discharge Channel, so make sure to stop by.
*Observation tours at the Metropolitan Area Outer Underground Discharge Channel require advance reservations. For details, please check the official website.

Photograph provided by Edogawa River Office, Ministry of Land, Infrastructure, Transport and Tourism