The underground cathedral protecting Tokyo from floods (2018)
31 comments
·July 10, 2025srvmshr
I have been to this place.
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.
userbinator
It must be the lighting and colouration, as your first two photos actually look like CGI or some sort of painted art.
bschwindHN
Weird, I visited last year and don't remember having a hard time getting tickets. Maybe I got lucky.
Here are a couple photos I took with people for scale:
jonnybgood
I've also visited. It was a hot day when I went. As we descended, the coolness felt amazing, but there was this misty fog inside. Mixed with the dark dampness, I felt like I walked in to a Andrei Tarkovsky scene.
whtrbt
I've also been (December 2024), I didn't realise it was so difficult to get reservations.
It is an awesome space and surprisingly well lit.
oceanhaiyang
And you gotta speak decent Japanese or have someone with you who does in case of emergency!
Those pictures look unreal!
Aeolun
They’re making more too! We got a new underground tank underneath the park nearby that they’ve been working on for years.
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.
realo
I have to mention here that 1,500 years ago the same was done in Istanbul:
yubblegum
It's in a James Bond film. Goes right under the Soviet embassy. /g
bobthepanda
Cisterns aren’t really the same thing; cisterns store drinking water for long term whereas these caverns are only supposed to hold water until the treatment plant can handle it.
geraldmcboing
It has a fantastic reverb too! Would love to take a drum kit down there... and a speaker to play a sweep & capture an IR. Tried using handclaps when I visited.
gnabgib
(2018) Discussion at the time (127 points, 30 comments) https://news.ycombinator.com/item?id=18570076
There was also a good NYT article in 2017 (293 points, 210 comments) https://news.ycombinator.com/item?id=15436943
NaOH
More:
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.
hinkley
The scale of this facility is deceptive in the video. If you pay attention about halfway through, a man walks through. His head only comes up almost to the top of the taper on the footings.
bastawhiz
It's not the same, but this is similar to Chicago's Deep Tunnel Project. There's a lot of fascinating reading on the project. If you're in the area, you can even get a tour of one of the stations:
acyou
22 meters underground, built in 1950s, Tokyo, 5-7% of GDP - yeah the gigantic underground vaults serve as flood protection, to those who have a good understanding of Japanese history, it's understandable to believe these were rather primarily built as bomb and nuclear shelters.
hollerith
It would easy to tell: (unless they were occupied by only a handful of people) they would be useless as fallout shelters without a lot of ventilation, and you can't rely on the wind: you'd need big fans and ducts, and the fans would need to keep running after most of the electricity-generating capacity available in Tokyo is destroyed, i.e., this ventilation system would need its own hardened electricity supply.
bobthepanda
Also, using this as a shelter would have a pretty obvious downside if torrential rainstorms happened.
tharkun__
Never mind all the wasted space above peoples' heads. The picture further down has people walking. They're tiny.
FigurativeVoid
Incredible.
I sometimes forget that manga writers use very real locations as references. I believe this is the backdrop for several Tokyo Ghoul scenes.
cobalt
it was also in mirror's edge, and several other pieces of media
c-hendricks
The Host also uses a similar setting for a good portion of the movie (from what I remember)
GrifMD
Mirror's Edge (2008) had a pretty neat level inspired by these storm drains https://www.youtube.com/watch?v=IE3qooY0d_A
HPsquared
Those columns are holding up the ceiling, and all the earth above.
G-Cans is impressive but there's a lot more than this protecting Tokyo from floods. A 100yrs ago they build the Arakawa river for flood control
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.