Located 50 metres below the ground in Kasukabe, Saitama Prefecture, the Metropolitan Outer Area Underground Discharge Channel (首都圏外郭放水路) is a disaster-prevention facility built to safeguard against flooding in the Greater Tokyo Area. A bit of a tongue twister in either language, the facility is also unofficially known as the G-cans, which, for brevity, is what I will refer to it as for the remainder of this article.
The G-cans is one of the largest underground drains in the world, with tunnels spanning 6.3 kilometres and an 18-metre high pressure adjusting tank that is 177 m long and 78 m wide.
The latter is what forms the main attraction for tours around the facility due to its resemblance to a cool-looking massive underground temple. Its dystopian appearance makes it a great location for shooting films, including the 2015 movie The Hunger Games: Mockingjay – Part 2.
Overview of the G-cans
The role of the G-cans facility is basically to channel water from small rivers into the Edogawa River whenever they threaten to overflow. There are four shafts that connect to one or two smalls rivers from which water automatically flows when the water level rises to a particular level. The fifth shaft doesn’t connect to any river but to the pressure-adjusting tank. The shafts are all connected via tunnels.
The pressure-adjusting tank, aka the “underground temple,” consists of 59 colossal pillars each weighing 500 tonnes. Water accumulates in this giant pool to reduce the momentum of the water flowing from the tunnels.
On the other side of the tank is a drainage pump station, which is controlled from the central control room in the administrative building. Pumps work to send water into the drainage sluiceway, which then flows into the Edogawa River.
Tours of the G-cans
There are three types of tours available for booking at the facility. All participants must first sign in at Ryu-Q-Kan (龍Q館), the museum of the facility, at least 10 minutes before the tour on the day.
Underground Temple Course
Cost: 1,000 yen
Duration: 55 minutes
Max participants: 50 people
This condensed tour takes you through the main water tank, where participants can also see the No. 1 shaft. You will need to descend down around 100 stairs to reach the tank. Once reassembled, staff will explain the mechanism of the underground channel before giving participants around 20 mins free time to take photos.
Pump Facility Course
Cost: 2,500 yen
Duration: 100 minutes
Max participants: 20 people
The tour is for mech fans and those interested in the specific workings of the underground channel. Participants can see the pump room and gas turbines, in addition to the main tank. The outer drainage channel utilises four large centrifugal pumps and four gas turbines.
Cost: 3,000 yen
Duration: 110 minutes
Max participants: 20 people
This is most expensive and comprehensive tour offered by the facility. In addition to the tour of the tank, participants also will be able to use the “catwalk” (a walkway for workers) and descend partway down the No. 1 shaft via stairs. The No. 1 shaft is around 70 m deep, with an internal diameter of 30 m. Wearing a helmet and harness is mandatory.
How to book
You can make bookings on the official website, in English or Japanese, up to a day prior. Cancellations through the website can be made up to three days prior without any penalty. From two days prior, a 100% cancellation fee is charged.
Getting to the G-cans
The closest station, located a 25-minute walk away, is Minami-Sakurai on the Tobu Urban Park Line. Public transport to the facility is scarce. There is a bus that runs very infrequently that will take you to the facility in 8 mins. You can check the timetable here. The fare is 150 yen, and you get off at the stop “龍Q館 (Ryu-Q-Kan).” Otherwise, your best option is to just walk the 2.3 kilometers from the station, or take a taxi if you don’t mind splurging.
720 Kamikanasaki, Kasukabe-shi, Saitama Prefecture