It is limited viewing, requires a reservation & the slots run out practically in seconds. Tough for us residents to get it as well. My wife could snag it in her third try, as a late birthday trip last year.
It is gargantuan & having massive holding capacity. To give semblance with something familiar, it was like standing in NY Grand Central station, except it was felt bigger, empty, damp & illuminated by floodlights from all sides. It is probably one and half football fields in length & scales high as much as a five storied building. Uploaded three pics to show the scale of this megalith. (The base of the pillars here are taller than average height of person to give a rough scale. The stairs come down from the ground level)
https://i.imgur.com/Jtcy0Ct.jpeg https://i.imgur.com/8Q08eKS.jpeg https://i.imgur.com/y75sfGP.jpeg
In addition to this underground chamber, there are two massive pumps on either sides, which divert the water from whichever river is surging to the other (Arakawa & Edogawa possibly). The chamber is the buffer zone between the rivers, not a storage tank ultimately. I was told by the civil engineer of this plant they could pump out as much as a jumbo jet's volume per minute in its storm surge channel/drain to manage flooding. You can walk up to the turbine room at the end of this room, and see its massive blades at an arm length. All with earthquake protection in place as well. Honestly mind-blowing piece of engineering.
Those pictures look unreal!
It is an awesome space and surprisingly well lit.
Here are a couple photos I took with people for scale:
I sometimes forget that manga writers use very real locations as references. I believe this is the backdrop for several Tokyo Ghoul scenes.
I guess it’s connected to this one, though I can’t find any information on that reservoir in specific.
https://sushitech-startup.metro.tokyo.lg.jp/sightseeing-tour...
It’s pretty relevant as my house is about 50m from that river.
https://www.youtube.com/watch?v=y3tdYolqiU8
Also, the rivers around Tokyo all have giant flood areas (parks, golf courses, farms) they can open to hold water in an emergency.
gnabgib•8h ago
There was also a good NYT article in 2017 (293 points, 210 comments) https://news.ycombinator.com/item?id=15436943
NaOH•5h ago
Tokyo Metropolitan Area Outer Underground Discharge Channel - https://news.ycombinator.com/item?id=43816183 - April 2025 (6 comments)
Tokyo expands underground 'temple' complex to counter climate change rains - https://news.ycombinator.com/item?id=41727317 - Oct 2024 (2 comments)
Tokyo's Underground Discharge Channel - https://news.ycombinator.com/item?id=19785044 - May 2019 (42 comments)
That second listing links to a piece with lots of good photographs.