Behold the awe-inspiring underground temple that protects Tokyo — reservations required on the official website!

The recommended transportation route to the Metropolitan Area Outer Underground Discharge Channel is to take the Tobu Noda Line to Minami-Sakurai Station, then walk for 40 minutes or take a bus (Kasukabe City Shōwa Area Loop Welfare Bus) to “Ryūkyūkan” (the exhibition hall of the discharge channel). Note that the bus service runs infrequently, which can be quite problematic — I’ll explain this in detail later, but in short:
There are no buses returning from Ryūkyūkan to Minami-Sakurai Station, so you’ll need to find a way to reach Ryūkyūkan first if taking the bus back. (The bus schedules do not align well.)
Walking the 40-minute route to Ryūkyūkan is extremely demanding, so most people opt to take a taxi from in front of Minami-Sakurai Station.

On the day of our visit, we departed from Asakusa Station on the Tobu Railway, transferring in Kasukabe just before reaching Minami-Sakurai Station. Seeing Kasukabe instantly brought to mind the Defense Force...

At the north exit of Minami-Sakurai Station, there are taxis available for hire. Simply tell the driver “Ryūkyūkan” (りゅうきゅうかん) and they’ll know where to go. I’ve forgotten the exact fare, but it was around 1,500 yen or so.

The exterior of “Ryūkyūkan” (りゅうきゅうかん). Opened in 2005, this water management exhibition hall is normally free to enter (though visiting the pressure-regulating water tank requires advance online reservation).

After climbing a long flight of stairs, we arrived at the second floor, where a large sign reading “見学会受付” (Public Tour Reception) was posted along the wall beside the staircase.

The second floor houses an exhibition hall featuring various models that demonstrate the workings of hydraulic engineering.

First, we checked in by providing the name of the person who made the reservation. The staff verified our names on the list, then handed us a consent form and a set of guidelines. That day, I visited with two family members, and since we were considered one group, we only needed to submit one consent form.

The visitor guidelines are very strict — it’s essential to follow the instructions of the tour guides at all times.

Our three tour admission badges. These can be kept as souvenirs after the tour, though the badge holders must be returned to the staff.

Since we were foreigners, they gave us special name tags and assigned a staff member who spoke a bit of English to accompany us. However, as my Japanese was sufficient for communication, she never actually spoke English — she explained everything in Japanese and asked me to translate each instruction to my family members who didn’t understand Japanese. She wouldn’t proceed to the next point until I had translated the previous one. This really showed how meticulous and serious Japanese work ethics are.
Honestly, visiting here might not be ideal if you don’t speak any Japanese...

The central control room that monitors the Metropolitan Area Outer Underground Discharge Channel.

The glass in the control room features an original Crayon Shin-chan (Crayon Shin-chan) illustration, depicting the Nohara family inside the pressure-regulating water tank of the discharge channel.

At 11:00 sharp, the guided tour began with a promotional video introducing the Metropolitan Area Outer Underground Discharge Channel.

The staff then explained the rivers connected to the discharge channel and the areas it helps protect from flooding.

Next, dynamic models inside the hall demonstrated how the discharge channel operates.

Through the dynamic model displays, it became very clear how floodwaters flow from intake shafts into the pressure-regulating water tanks.

An introduction to the water pump motors.

Introduces entertainers who have filmed at the underground temple of the Metropolitan Outer Area Underground Discharge Channel, complete with photos and autographed boards.

There are a huge number of them!! And amazingly, even foreign singers have shot MVs here.

Next, the staff took us to the rooftop of the Ryugaku Kan (Dragon Learning Hall), where we looked down over the entire Edogawa River basin. Before going up, the staff reminded everyone that it would be very cold outside and advised us to dress warmly. It was winter at the time, but the weather was unusually nice—with bright sunshine. I thought, how cold can it be in the sun? I even felt the staff were being overly cautious.
But the moment we stepped onto the roof—oh my god!!! It was freezing!!! The temperature wasn’t extremely low (around 4 or 5 degrees Celsius) and the sun was out, but because there were virtually no tall buildings nearby, the wind on the rooftop was incredibly strong!!!! The wind chill must have been below zero… absolutely freezing.

Everyone endured the bitter cold and listened carefully to the explanation.

The weather was clear with excellent visibility, and we could see Mount Fuji in the distance.

Then we prepared to leave the Ryugaku Kan and head to the main attraction of the trip: the pressure regulating reservoir of the Metropolitan Outer Area Underground Discharge Channel.

This entrance, which looks like the gateway to a secret base, is actually the entrance to the pressure regulating reservoir of the Metropolitan Outer Area Underground Discharge Channel.

Before entering, the staff explained the regulations for visiting the pressure regulating reservoir, mainly that we couldn’t go beyond the areas designated by the guide, and that we couldn’t take photos while descending the stairs—we had to watch our steps to avoid falling.

After a long flight of stairs, we finally arrived at the pressure regulating reservoir of the Metropolitan Outer Area Underground Discharge Channel. At that moment, I was incredibly excited—because I had finally reached the place I’d been looking forward to for so long.

The pressure regulating reservoir is 177 meters long, 78 meters wide, and 18 meters high, supported internally by 59 massive concrete pillars. The staff gave an introductory explanation first, and after that, we began a self-guided tour. However, the area open for viewing was limited, roughly around the first three pillars at the front of the reservoir.

It really did have the feel of a temple, and also resembled scenes from sci-fi movies—it’s no wonder special effects dramas (tokusatsu) are filmed here.

During floods, the reservoir fills with water, and the puddles on the ground are leftovers from the last flood drainage.

After about an hour of the tour, the explanation ended, and we prepared to take the bus back to Minami-Sakurai Station. Originally, we had asked the staff to call a taxi for us. But then I suddenly spotted this bus stop.

Looking at the bus schedule, we could just catch the 11:44 bus to Harue-Nishiguchi, and get off at Minami-Sakurai-Kita. (We could’ve taken it all the way to the terminal, Harue-Nishiguchi—it’s only 100 yen anyway, right?)

We waited at the bus stop for quite a while, starting to worry if the bus would actually come… But a few minutes after 11:44, the bus finally appeared!!!! I was so relieved.

We got off at Minami-Sakurai-Kita.

After getting off, I thought—if there’s a bus from the Ryugaku Kan back to the station, then there must be one from the station to the Ryugaku Kan too. So I took a closer look at the bus schedule.

There are only two buses to the Ryugaku Kan, at 12:37 and 16:57.

Let’s check the bus times from the Ryugaku Kan back to Minami-Sakurai Station: they’re at 7:44 and 11:44. Wait a minute—that doesn’t line up!! The buses to the Ryugaku Kan only run in the afternoon, but the ones back to the station only run in the morning. For example, if I take the 12:37 bus to the Ryugaku Kan, there’s no bus to come back (the return buses are at 7:44 and 11:44), and it’s also hard to get a taxi at that time.

Therefore, I recommend the following transportation plan and reservation timing:
Reserve a 10:00 tour, take a taxi from Minami-Sakurai Station in the morning to the Ryugaku Kan, and after the visit, take the 11:44 bus back.
This is the transportation method and reservation time I recommend—please take it as a reference.
 

Kavana @ Kyoto Free Stay.