The Metropolitan Area Outer Underground Discharge Channel (首都圏外郭放水路) is the largest underground facility in the world to divert overflowing water from nearby rivers to prevent major flooding around the Kanto region. It is located at Kasukabe, Saitama prefecture, which is close to the border of Tokyo.
The most impressive part of this facility, is the surge tank to divert the floodwater, nicknamed “The Underground Temple”.
Due to the large volume of water pressure it retains during operation, each pillars weighed 500 ton and 18m tall, creating this menacing look.
By comparison, human looks tiny when standing next to the pillar.
When not in operation, the public can actually visit the underground facility with prior reservation.
Please take note however, this tour is offered in Japanese language only as they do not have guide in English. Therefore the visit must be accompanied by someone who can understand Japanese.
The facility’s website in English: