The underground cathedral protecting Tokyo from floods (2018)

[srvmshr]

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.

[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:

https://imgur.com/a/DPYYou4

[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.

[bencyoung]

The Fens in East Anglia in the UK has a lot of interesting pumping tech. The latest can do 100m3/s (https://www.edie.net/st-germans-pumping-station-keeps-fens-f...). If all the pumps failed there would be hundreds of km2 underwater within days or weeks

[left-struck]

> 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).

You probably mean pumping stations right? Usually single pumps don’t have that kind of flow rate. Just a nit pick though, your comment was really interesting!

[userbinator]

It must be the lighting and colouration, as your first two photos actually look like CGI or some sort of painted art.

[oceanhaiyang]

And you gotta speak decent Japanese or have someone with you who does in case of emergency!

Those pictures look unreal!

[BeFlatXIII]

The one with the stairs could've been ripped straight from the original Half-Life. Makes me want to play it again. Thank you for the reminder.

[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.

[rayiner]

I love civil engineers.

[tonyhart7]

are you japanese ??? or foreigner that marry local?

[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.

[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.

[realo]

I have to mention here that 1,500 years ago the same was done in Istanbul:

https://en.m.wikipedia.org/wiki/Basilica_Cistern

[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.

[yubblegum]

It's in a James Bond film. Goes right under the Soviet embassy. /g

[GrifMD]

Mirror's Edge (2008) had a pretty neat level inspired by these storm drains https://www.youtube.com/watch?v=IE3qooY0d_A

[Lammy]

So does Splatoon 3 https://splatoonwiki.org/wiki/Undertow_Spillway

[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:

https://mwrd.org/locations/tarp-mainstream-pumping-station

[femto]

In a similar vein is the surge shaft being built as part of the Snowy 2.0 scheme in Australia. 28 metres diameter and 263 metres deep. It absorbs the momentum of the surge of water when the downstream power station closes its valves.

https://www.snowyhydro.com.au/wp-content/uploads/2024/01/SH_...

[cesarb]

> In a similar vein is the surge shaft being built as part of the Snowy 2.0 scheme in Australia. [...] It absorbs the momentum of the surge of water when the downstream power station closes its valves.

Not the same power station, but I have to post a link to one of my favorite YouTube videos: https://www.youtube.com/watch?v=fJVBlhgt9j8 (Obere Wasserschlosskammer).

[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)

[otikik]

Japan is a great place to visit if you are even slightly interested in infrastructure.

The earthquakes make it so that what would be a simple overpass has all of this ... stuff that would not exist in a more geologically stable region.

Culture and food were still my main motivations for visiting, but the infrastructure part came as a nice bonus.

[tecleandor]

There's is an official version in Minecraft, if you feel like visiting from home:

https://www.ktr.mlit.go.jp/edogawa/edogawa01318.html

[HPsquared]

Those columns are holding up the ceiling, and all the earth above.

[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.

[socalgal2]

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.

[BeFlatXIII]

> “It’s like a science-fiction kind of facility,” says JICA’s Inaoka, whose job involves collaborating with experts from developing countries to share Japan’s expertise.

My first thought upon seeing the photos was that this was the inspiration for many of the indoor levels in the original Half-Life. All that's missing are the headcrabs.

[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.

[aikinai]

Can't believe no one has mentioned the Great Hall of Moria[0]. I always thought it was uncannily similar.

[0] https://imgur.com/a/OHKifqj

[PapstJL4U]

Colour it green and you have a Mirrors Edge Level - this really looks like the underground part in the first game. The form of the stele as an example.

I am sure other cities have it as well, but it really looks close to the level.

[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.

[yason]

If anyone has a link to a video (or time in a video) where this thing fills up, please share.

[ykonstant]

Even the word "cathedral" doesn't do justice to that structure.