Located 50 meters underground in Kasukabe, Japan, the Metropolitan Area Outer Underground Discharge Channel—commonly known as G-Cans—is the world's largest subterranean flood containment facility. Completed in 2006 after 13 years of construction, this colossal engineering marvel was built to shield Northern Tokyo from the devastating overflow of five local rivers during heavy typhoon seasons. The system functions by redirecting floodwaters through five massive vertical shafts, each large enough to fit the Statue of Liberty inside.
Water travels through a 6. 3-kilometer underground tunnel network into a gigantic surge tank nicknamed the 'Underground Temple.' This main reservoir spans 177 meters long and 78 meters wide, supported by 59 massive concrete pillars weighing 500 metric tons each.
Once collected, high-powered turbine pumps driven by modified aircraft gas engines discharge up to 200 cubic meters of water per second into the Edo River, effectively draining an Olympic-sized swimming pool in just 12 seconds. Beyond its critical infrastructure role, the eerie, cathedral-like aesthetics of the surge tank have turned G-Cans into a pop-culture icon, serving as a popular film set for sci-fi movies, television shows, and music videos.