The system acts as a giant subterranean reservoir, often referred to as the 'Underground Temple' due to its massive concrete pillars.
It is the world's largest underground discharge channel, constructed to divert water from smaller rivers in the Saitama area.
The surge tank is 177 meters long and 78 meters wide, featuring a depth equivalent to a 20-story building.
The water discharge process utilizes aviation-grade gas turbine engines to power the massive drainage pumps.
The museum serves as the entry point for the guided tour and provides technical documentation on the engineering feats required for construction.
The facility is sometimes used as a location for science fiction films, music videos, and high-fashion advertisements due to its unique architectural geometry.
During peak rainy seasons, tours are frequently suspended or canceled on short notice to ensure the facility is ready for emergency flood management.
The Underground Exploration Museum RYU-Q Kan provides public access to the Metropolitan Area Outer Underground Discharge Channel, a massive flood prevention system designed to protect Tokyo from typhoon-induced overflows. The facility features a museum exhibition area followed by a guided descent into the G-Cans project's central pressure-adjusting water tank. This infrastructure consists of five containment silos connected by 6.3 kilometers of tunnels located 50 meters underground. The cavernous tank is supported by 59 massive concrete pillars, each weighing 500 tons. It functions as a surge tank to mitigate water pressure from the tunnels before discharging into the Edo River. Operations are strictly dependent on weather conditions and flood risk status, as the infrastructure must be functional for disaster prevention.
The base of the surge tank, looking up at the grid of 59 massive support pillars.
Book your guided tour reservation well in advance through the official website, as walk-ins are generally not accommodated.
Check the facility status on the morning of your visit, as tours are canceled whenever the system is activated to prevent flooding.
Wear comfortable, non-slip walking shoes, as the tour involves traversing metal catwalks and steep stairs.
Do not attempt to visit without a pre-confirmed reservation; arriving without one will result in being denied entry.
Closed on Mondays and occasionally on Tuesdays if Monday is a public holiday; operations are suspended indefinitely during flood alerts or maintenance cycles.
Participants must follow the guide's instructions at all times and remain within designated tour pathways for safety.
