A man-made cave of wonders: the world’s biggest underground storm drain in Kasukabe

By Fran Wrigley

Deep beneath the ground, 32 kilometers north of Tokyo, lies a truly incredible feat of engineering. The G-Cans Project is the largest storm drain on earth, a colossal series of underground silos and tunnels, built to protect Tokyo from flooding during typhoon seasons. Its main hall (actually an enormous water tank) is held up by 59 columns each 25 meters high, and is known as the “Underground Temple”.

The facility is free to visit by guided tour, and the folks at Another Tokyo, a Japanese website introducing off-the-beaten-track places from around the country, recently went to check it out.

G-Cans (Shutoken Gaikaku Hosuiro, or the Metropolitan Area Outer Underground Discharge Channel) is located in Kasukabe in eastern Saitama. The area is historically prone to flooding, and the G-Cans facility collects storm water from no less than five different rivers. It cost over 200 million yen and took 17 years to construct, being completed in 2009. Due to its epic proportions and all-round underground spookiness, it has also been used as the setting for TV shows and commercials.

The facility is accessible via the underground exploration museum “Ryukyukan” (龍Q館). Tours are free, but must be booked in advance. Your ticket doubles as a souvenir postcard.

The facility is made up of five concrete containment silos, 65 by 32 metres, connected by six kilometers of tunnels. It’s this main water tank, the so-called “Underground Temple”, which is the real showstopper though. At a height of 25 meters, and stretching for 177 meters, the visiting people are dwarfed by the sheer scale of it.

Storm water flows into the facility through five cylindrical shafts. The ceiling is held up by 59 enormous pillars. Each weighing 500 tons, these also function as weights, preventing the tank, which is as large as a football pitch, from rising towards the surface.

Tours operate three times a day, but only on weekdays – in fact, only Tuesday to Friday.

There is some English information available on the official website; however, there are no English tours, and if you don’t understand Japanese, the organisers require that you bring an interpreter.

Oh yeah, and access to the main surge tank is cancelled when it’s “in use”. Well, you wouldn’t want to be in there with all that water, would you?

Source and image: Another Tokyo Additional sources: Shutoken Gaikaku Hosuiro Official Site, Atlas Obscura

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A storm sewer called, "Ryukyu"... wow Tokyo. That's like a city dump in North Carolina called Cherokee.

-10 ( +0 / -10 )


2 ( +2 / -0 )

They drove a Range Rover through there a few years ago for a TV commercial.

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Katie, the article didn't say the storm sewer is called Ryukyu. It said the tour of the storm drain is accessed through a museum called Ryukyukan. The kanji for the museum means "dragon museum", I think. The kanji for Ryukyuan, the people native to the islands south of Japan, is different. So no, it isn't like a city dump being called Cherokee. Not even close. Anyway, I have seen this on TV a few times, it was featured on a BBC documentary I saw. However, the documentary just said it was in Tokyo, I didn't know it was in Kasukabe! I used to work in that city! I wish I would have known it was there and I could take a tour. I no longer in Japan, but maybe some day I can come and tour the facility. It is very impressive!

5 ( +5 / -0 )

This was featured on the Discovery Channel. Many big metropolitan areas are employing this type of system or comparable ones to ward off flooding.

1 ( +1 / -0 )

Underground Temple! Engineering, it is.

1 ( +1 / -0 )

Katie, the museum is called 龍Q not 琉球. Japanese has many, many homonyms! That first kanji in 龍Q means dragon.

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Katie Haigh

A storm sewer called, "Ryukyu"... wow Tokyo. That's like a city dump in North Carolina called Cherokee.

RME... First day in Japan?

1 ( +2 / -1 )

I have visited this amazing facility and was extremely impressed by not only scale but that it can save the below sea level areas of Tokyo from being flooded by the 5 rivers that flow from other prefectures. The bus tour showed us the raised banks that protect areas along the rivers, too, and we were told about the various drills among citizenry in case of floods and tsunamis. There were boats in boxes that could hold 4-5 passengers and collapse again after use. Extremely impressive. On the surface of the protective banks, kids play soccer and people fly remote controlled airplanes. Pretty beautiful area. I'd love to visit again.

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