Explore the “Underground Temple” of the Metropolitan Area Outer Underground Discharge Channel in Saitama Prefecture! Learn about the operation of this world-class flood control facility, how to book a tour, and witness Japan’s disaster prevention engineering marvel.
Introduction
Hidden beneath the bustling Tokyo metropolitan area lies a colossal space straight out of a science fiction movie – massive pillars stand in rows, extending to the horizon, exuding a solemn and mysterious aura, earning it the nickname “Underground Temple.” This is not an ancient ruin but a marvel of modern engineering that protects the lives and property of countless residents: the Metropolitan Area Outer Underground Discharge Channel. Located in Kasukabe City, Saitama Prefecture, this world’s largest underground drainage system is not only a symbol of Japan’s cutting-edge disaster prevention technology, but its unique and spectacular internal view has also become a popular visiting spot in recent years, attracting many films and dramas for location shooting. This article will take you deep into this mysterious “Underground Temple,” explaining its construction purpose and astonishing functions, exploring the awe-inspiring space of its core facility, the “Pressure Adjusting Water Tank,” introducing how to book a tour to see this grand project, and providing detailed transportation and visiting information, allowing you to glimpse this underground fortress that guards the metropolitan area.
The Underground Great Wall Guarding the Metropolitan Area: Construction Purpose and Operating Principles
The birth of the Metropolitan Area Outer Underground Discharge Channel is a response to the long-standing flood threats that have plagued the local residents.
Why Was This Underground Great Wall Needed?
- Low-Lying Terrain Challenge: The eastern part of Saitama Prefecture, especially the Naka River and Ayase River basin around Kasukabe City, has relatively low and flat terrain with gentle river gradients, making drainage difficult. When typhoons or concentrated heavy rainfall occur, the water from upstream tends to converge here, causing rapid rises in the water levels of small and medium-sized rivers (such as the Ootoshi-Furutone River and Kuramatsu River), frequently leading to floods that severely impact residents’ lives and urban functions.
- Impact of Urbanization: With the development of urbanization, the area covered by concrete has increased, making it difficult for rainwater to infiltrate the ground, further increasing the risk and scale of floods.
A World-Class Flood Control System
To solve this long-standing flood problem, the Japanese government spent approximately 13 years (construction started in 1993, major parts completed in 2006) and invested vast sums to build this massive underground discharge channel system, reaching 50 meters underground. Its operating principles are as follows:
- Water Intake (Intake Facilities/Vertical Shafts): When the water levels of the surrounding small and medium-sized rivers exceed the warning line, the floodwater automatically flows into the five massive vertical shafts (each about 70 meters deep and 30 meters in diameter, large enough to accommodate the Statue of Liberty or a space shuttle!) installed along the route.
- Water Guidance (Tunnel): These vertical shafts are connected by a massive underground tunnel, 6.3 kilometers long and about 10 meters in internal diameter. The floodwater converges and flows in the tunnel.
- Pressure Adjustment (Pressure Adjusting Water Tank – Underground Temple): The floodwater finally flows into the massive pressure adjusting water tank, nicknamed the “Underground Temple.” This space is 177 meters long, 78 meters wide, and 18 meters high, with 59 massive pillars weighing 500 tons each supporting the ceiling. Here, the floodwater slows down and stabilizes its pressure, preventing direct impact on the drainage facilities.
- Drainage (Drainage Pump Station/Drainage Gate): Finally, using four massive pumps modified from aircraft gas turbine engines (drainage pump station), the floodwater stored in the pressure adjusting water tank is powerfully discharged into the Edogawa River, which has a wider channel and stronger drainage capacity. This effectively lowers the water levels of the surrounding rivers, achieving the goal of flood defense or disaster mitigation.
This massive system is activated approximately 7 times a year on average, silently protecting the safety of the metropolitan area.
Descending into the “Underground Temple”: The Awe-Inspiring Space of the Pressure Adjusting Water Tank
The most captivating part of the Metropolitan Area Outer Underground Discharge Channel, and the main destination for general tours, is the Pressure Adjusting Water Tank, affectionately known as the “Underground Temple.”
Overwhelming Sense of Scale
- Size: Measuring 177 meters long, 78 meters wide, and 18 meters high, its area is equivalent to about two soccer fields. When you descend the 116 steps from the ground-level entrance and step into this space located 22 meters underground, you will first be struck by its astonishing scale.
- Forest of Giant Pillars: 59 massive concrete pillars, 18 meters high and weighing 500 tons, are neatly arranged, supporting the vast ceiling. Standing next to the pillars, people appear incredibly small, creating a solemn, even surreal atmosphere reminiscent of ancient Greek or Egyptian temples.
- Light, Shadow, and Silence: When not filled with water, the space appears vast and silent, with only the sound of visitors’ footsteps and the guide’s voice echoing. The limited lighting and the light filtering down from the ground entrance create unique light and shadow effects, further enhancing the sense of mystery.
Filming Location for Films and Art
Due to its unique and visually impactful spatial quality, the pressure adjusting water tank is often used as a filming location for movies, TV dramas, special effects shows (like Kamen Rider), music videos, etc., adding a cultural and artistic charm beyond its function as an engineering facility.
Exploring the Underground World: Booking a Tour
To personally experience the awe of the “Underground Temple,” you must participate in officially organized guided tours. Visits are by reservation only and cannot be booked on the spot.
Types and Features of Tours
Currently, several different tours with varying content and depth are offered (tour content and fees are subject to change; please check the official website).
- Underground Temple Course (地下神殿コース):
- The most basic and popular tour.
- Content: Visit the operation room and the “Ryukyukan” museum on the ground level, and walk into the Pressure Adjusting Water Tank (Underground Temple).
- Duration: Approximately 55-60 minutes.
- Fee: Approximately 1,000 JPY/person.
- Restrictions: Open to elementary school students and above (elementary students must be accompanied by an adult).
- Vertical Shaft Experience Course (立坑体験コース):
- Offers a deeper experience of the facility.
- Content: Includes the Underground Temple Course content, plus a visit to the upper space of the First Vertical Shaft (looking down into the 70-meter deep shaft from above).
- Duration: Approximately 100-110 minutes.
- Fee: Approximately 3,000 JPY/person.
- Restrictions: Open to 4th-grade elementary students and above, and must be accompanied by an adult.
- Pump Appreciation Course (ポンプ堪能コース):
- Focuses on visiting the drainage facilities.
- Content: Includes the Underground Temple Course content, plus a visit to the pump room (where you can see the massive pump equipment) and the backflow prevention gate, etc.
- Duration: Approximately 100 minutes.
- Fee: Approximately 2,500 JPY/person.
- Restrictions: Open to elementary school students and above (elementary students must be accompanied by an adult).
- Impeller Exploration Course (インペラ探検コース):
- The newest and most in-depth tour.
- Content: Includes the Underground Temple Course content, plus wearing special gear and actually entering a deeper part of the Pressure Adjusting Water Tank to see the massive impellers connected to the drainage pumps up close.
- Duration: Approximately 110 minutes.
- Fee: Approximately 4,000 JPY/person.
- Restrictions: Open to 4th-grade elementary students and above, and must be accompanied by an adult.
- 【New】Underground River Walking Adventure Experience Course (地下河川ウォーキングアドベンチャー体験):
- A special tour starting from April 2025 (limited availability each month).
- Content: Wearing wading gear and actually walking into a part of the underground tunnel connecting the Third Vertical Shaft and the Pressure Adjusting Water Tank.
- Duration: Approximately 4 hours.
- Fee: Approximately 15,000 JPY/person.
- Restrictions: Must meet specific physical fitness and safety requirements.
How to Book?
- Official Website Reservation: All tours must be booked online through the official Metropolitan Area Outer Underground Discharge Channel tour website.
- Booking Period: Bookings are usually available for tours within one month. Slots for popular times (such as weekends and holidays) or special tours are limited, so early booking is recommended.
- Language: The guided tour is primarily in Japanese. Audio guides in English or other languages may be available for some tours (please check). At least one person in the group must be able to understand the staff’s instructions in Japanese (related to safety matters).
Practical Information: Transportation, Fees, and Precautions
Transportation Methods:
- Train + Bus/Walk (Main Method):
- Take the Tobu Urban Park Line to “Minami-Sakurai Station“.
- From the North Exit of Minami-Sakurai Station, take the Kasukabe City Community Bus “Haru Bus” (bound for “Showo Sogo Shisho”) and get off at the “Ryukyukan” stop, which is right there (approx. 7-10 minutes ride, buses are not frequent).
- It takes about 30-40 minutes to walk from the North Exit of Minami-Sakurai Station (approx. 3 km).
- It takes about 7 minutes by taxi from the North Exit of Minami-Sakurai Station.
- By Car: Head there via National Route 16. Free parking is available.
Tour Fees:
- As mentioned above, fees vary depending on the tour (ranging from approximately 1,000 to 15,000 JPY). Fees may change, so please check the official website at the time of booking.
Ryukyukan (Underground Exploration Museum):
- The management facility located on the ground level, also serving as the check-in and meeting point for tours.
- The building houses exhibition rooms introducing the structure, function, and history of the Metropolitan Area Outer Underground Discharge Channel, and you can also see the operation room (included in some tours). Even if you don’t participate in the underground tour, you can visit some areas of the Ryukyukan for free.
【Important!】Visiting Precautions:
- Safety First: Visiting tours involve entering underground facilities, so you must follow the staff’s instructions at all times.
- Stairs: You need to ascend and descend over 100 steps on your own to reach the Pressure Adjusting Water Tank (Underground Temple). There are no elevators or escalators. Visitors with mobility issues may not be able to participate.
- Footwear: The ground inside the underground facility may be wet and slippery, and there are grated floors. Wearing high heels, sandals, or shoes with slippery soles is prohibited. You must wear non-slip, closed-toe athletic shoes or flat shoes.
- Clothing: Wearing comfortable pants that you don’t mind getting dirty is recommended. The temperature underground may be low, so bringing a light jacket is advisable even in summer.
- Age Restrictions: Each tour has different age restrictions (generally elementary school students and above, with some tours requiring 4th-grade elementary students and above), and children must be accompanied by an adult.
- Language Proficiency: As mentioned earlier, at least one person in the group must be able to understand safety instructions in Japanese.
- Tour Content Change or Cancellation: Tours (especially the underground portion) may be temporarily changed or canceled due to heavy rain, actual facility operation (drainage), or other safety factors. Please be aware of this possibility.
- Prohibited Items: Large luggage, tripods, selfie sticks, dangerous items, etc., are prohibited from being brought underground.
- No Eating or Smoking: Eating and smoking are prohibited within the facility.
Conclusion
The Metropolitan Area Outer Underground Discharge Channel, this “Underground Temple” hidden beneath the earth for disaster prevention, is not only a grand engineering feat that protects countless people from the threat of floods, but its spectacular spatial structure also offers an incredible visual impact and an extraordinary experience. Descending the hundred steps yourself and stepping into the sacred space formed by the colossal pillars will allow you to deeply appreciate the mastery of human engineering and the wisdom in confronting natural disasters. Through booked guided tours, we can glimpse the mysterious veil of this underground fortress and understand its operating principles and importance. If you are interested in large-scale engineering, disaster prevention facilities, or are looking for a unique and visually impactful visiting spot, the Metropolitan Area Outer Underground Discharge Channel is definitely a place worth planning a deep exploration trip to and witnessing this underground marvel that protects the metropolitan area firsthand!
Which tour of the Metropolitan Area Outer Underground Discharge Channel are you most interested in? Do you want to see the magnificent “Underground Temple” with your own eyes, or do you want to explore the vertical shafts or pump facilities more deeply? If you found this article helpful in understanding this special spot, please share it with friends who are also interested in engineering marvels!
