An Underground Cathedral of Engineering
The Metropolitan Area Outer Underground Discharge Channel, often called G-Cans Tokyo, is a vast underground flood-control system built by the Ministry of Land, Infrastructure, Transport and Tourism. Built on the outskirts in northern Tokyo, it protects millions of residents by capturing and redirecting dangerous stormwater before it reaches the city.
A Subterranean Space Like No Other
Started in 1992 and operating since 2006, G-Cans diverts excess stormwater into a vast network of tunnels and chambers buried roughly 50 meters below ground. At its core is a massive pressure-adjustment water tank — often called the “underground temple” — that measures approximately 177 meters long, 78 meters wide, and 25 meters tall and is supported by 59 towering concrete pillars.
The entire system includes five cylindrical concrete silos more than 65 meters deep and 32 meters in diameter, connected by over 6 km of reinforced underground tunnels. These silos collect stormwater overflow from rivers like the Naka, Kuramatsu, Arakawa, and Nakagawa before channeling it toward the central reservoir for controlled discharge.
A small entrance door on a non descript football fields leads into the hidden complex. After descending many levels of stairs one emerges within a space resembling a huge underground cathedral. Towering concrete pillars rise from the floor like ancient monoliths, forming a hall that extends into the darkness. The space is quiet, cool, and monumental—an engineered landscape that feels both futuristic and mythic.
On a sunny day it’s eerily calm inside, but traces of the ferocity of the water that flows through here during storms is evident. Fresh silt and mud streak down the walls and pools of murky water pond around the columns. Tours are allowed to proceed during the dry months, but in the rainy summer months access to the chamber is often closed.
Booking a Tour of G-Cans Tokyo
Visitors can book a guided tour of the Metropolitan Area Outer Underground Discharge Channel through the official reservation website operated by the Ministry of Land, Infrastructure, Transport and Tourism. Various tours are available from the standard Underground Temple Course (￥1000) to the longer Impeller Exploration course (￥4000) which only held a few times a month. Spaces fill quickly, so be sure to book in advance.
Tours begin in the main facility control building where you can view the control room and various exhibition spaces. The tour is conducted in Japanese, with a leaflet given for English speaking visitors. Previously foreign visitors needed a Japanese translator to be with them in order to visit, however this rule has been relaxed in recent years.
Location
Address:
首都圏外郭放水路
720 Kamikanasaki, Kasukabe, Saitama 344-0111, Japan
Getting there & Access
The building is located in central Tokyo and is a short walk from Tamachi / Mita stations.
Project Details
Photographs : © Finbarr Fallon (2024)
