Users rush to post and gush over photos of the waterlogged caverns beneath Japan’s Metropolitan Area.

The G-Cans project (Shutoken Gaikaku Hōsuiro, or the Metropolitan Area Outer Underground Discharge Channel) is something of a hidden treasure in its native Kusakabe, Saitama; and we do mean hidden literally. Tucked 5 meters (16.4 feet) underneath the ground lies a yawning labyrinth of empty tunnels spanning 6.4 kilometers (3.9 miles), supported by 59 gigantic pillars. Each pillar can pump roughly 200 tons of water per second into the nearby Edogawa River, and the corridors themselves run between five concrete containment tanks. The whole set-up took roughly 16 years from planning to completion, and cost upwards of 2 billion US dollars.

As its name suggests, the Underground Discharge Channel’s purpose is to divert excess water – say, from a sudden dramatic weather event – away from the streets and into its silos, whereupon the water can be rapidly pumped back out into the waiting river. And that’s exactly what happened here on October 12, when Typhoon Hagibis struck the Greater Tokyo Area with a vengeance.

Twitter user @yama_sato3, having toured the G-Cans project immediately after the typhoon hit, shared a series of photographs of the currently operating water silos. The initial tweet reads:

“[Metropolitan Area Outer Underground Discharge Channel] I participated in a tour here the day after Typhoon Hagibis passed. I’ve taken the tour twice before now, but never while it was in operation. The 70 meter passage accrued 55 meters of water… What would have even happened if we didn’t have this facility? Thank you, Underground Temple.”

The images continued to flow in the rest of the thread:

“[Metropolitan Area Outer Underground Discharge Channel] Here is the Underground Temple (Pressurized Water Tank) when empty of water. In it stand 59 pillars, each about 18 meters in height. The first passage is visible from the Underground Temple, but I chose to observe it from the upper catwalk instead. ([images from]November 2014)”

These images don’t only inspire awe from the gargantuan size of the tunnels and halls, but relief and gratitude that they managed to divert such a huge volume of water away from the streets of Saitama. Commenters conveyed their intense emotions accordingly:

“Amazing. A real masterpiece. I’m grateful to those from the past who made it happen.”
“Hey there! I saw this place on TV and wondered whether it ever actually got used, and how neat it’d be if when it got used someone could upload what it looked like. It saved the metropolitan area, didn’t it! Thanks, Underground Temple!”
“You went at the perfect time!”
“There’s a dungeon in Final Fantasy 14 called Pharos Sirius that looks like this, so when I saw this at first I was like ‘Wow, Pharos Sirius is real?!'”

When it’s not fulfilling its intended purpose, the G-Cans projects’ roomy hallways are either filled with visitors willing to pay the 3,000 yen entrance fee or busy with film crews. The titanic ceilings, eerie pillars and lack of natural light make it a great fit for music videos or spooky movie scenes, too. But you needn’t take our word for it – you can tour some of the tunnels yourself using nothing but Google Maps, and really throw its disaster relief role into perspective.

Source: Twitter/@yama_sato3 via Netlab
Featured image: Twitter/@yk_ichinomiya

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