From above ground, it's just a park. Lawns and soccer fields. But if you take a vertical staircase 50 meters underground from there, a completely different world appears. The sight of 59 concrete pillars, 18 meters tall, lined up in a space the size of two soccer fields – even from photos, I thought, "Is this really in Japan?" They say it's even more overwhelming in person.
Tokyo's low-lying areas suffered severe flooding damage during typhoons and heavy rains. The Japanese government spent 230 billion yen (about 2 trillion won) over 13 years to build this Outer Metropolitan Area Floodway. Instead of holding water, it's designed to swallow overflowing river water whole and discharge it into the Edogawa River. It's truly at the forefront of modern civil engineering.
Each Pillar Weighs 500 Tons
The structure of the Outer Metropolitan Area Floodway is overwhelming in its sheer scale. The core of the system, the Surge Tank, measures 177 meters long, 78 meters wide, and 18 meters high. This is larger than two average soccer fields combined.
Supporting this space are 59 colossal concrete pillars, each 18 meters tall and weighing 500 tons. Each pillar is equivalent to the weight of a large airplane, and the sight of these pillars standing at regular intervals is reminiscent of the Parthenon in Greece, earning it the moniker Underground Temple.
The entire facility spans 6.3 km and draws water through underground tunnels to prevent flooding in surrounding small and medium-sized rivers. Most astonishing is its drainage capacity. At the heart of this facility are four 14,000-horsepower gas turbine pumps, modified from aircraft engines. These pumps can discharge 200 cubic meters of water per second into the Edogawa River, an incredible performance capable of emptying a 25-meter swimming pool in just one second.
When Floods Come, This Machine Activates
The flood prevention system operates precisely in unseen depths. When river levels reach dangerous heights, the system protects the city through the following three-stage process:
Why Godzilla Was Filmed Here
Beyond its functional purpose, this facility has inspired countless artists with its unique engineering beauty. The overwhelming size of the concrete pillars, the cold air, and the geometric patterns created by light and shadow resemble a scene from a sci-fi movie.
In fact, it has been used as a filming location for special effects films like Godzilla and Kamen Rider, as well as numerous movies, commercials, and music videos. Game developers have even borrowed the imagery of this space to design dungeons featuring giant bosses. The name Underground Temple is not just due to its appearance, but because the awe and sacredness one feels upon entering it resemble that of religious architecture.
The Japanese government operates regular tours to promote the value of this facility. It is considered one of the most unique courses to experience during a Tokyo trip, and tens of thousands of tourists and civil engineering experts from around the world visit Saitama each year to see this magnificent disaster prevention facility.
Things to Know Before Visiting
It's located in Kasukabe City, Saitama Prefecture, over an hour by train from central Tokyo. You can get there by taxi or bicycle from Kasukabe Station's east exit. Be sure to check the shuttle bus schedule on the official website in advance.
You must make a reservation in advance on the official website to enter. During typhoons or heavy rain, the facility is actually in operation, so the tour itself will be canceled. It's cool 50 meters underground all year round, so even if you go in the summer, bring a light jacket, and sneakers are a must because there are many stairs and the floor can get wet. You can take photos inside the surge tank, but the use of tripods may be restricted, so please check.