Looming 50 meters beneath Kasukabe, Saitama, the Metropolitan Area Outer Underground Discharge Channel—popularly known as G-Cans—looks more like an ancient subterranean shrine than a modern engineering marvel. Built between 1992 and 2006 at a cost of roughly $2 billion, this immense facility was designed to protect the Tokyo metropolitan region from devastating typhoons and heavy monsoons. When torrential rains cause local rivers to overflow, floodwaters plunge into five massive underground containment silos.
Each concrete silo is 65 meters deep and 32 meters wide—large enough to easily swallow the Statue of Liberty. The collected water then travels through a 6. 3-kilometer network of subterranean tunnels driven by gravity into a colossal central surge tank.
This central chamber, dubbed the Underground Temple, spans 177 meters long and 78 meters wide. Its massive ceiling is supported by 59 concrete pillars, each standing 18 meters tall and weighing 500 tons. Beyond holding up the ceiling, these pillars prevent the empty tank from buoyant displacement caused by surrounding groundwater pressure.
To clear the water, G-Cans relies on four custom turbine pumps driven by modified Boeing 737 aircraft gas engines. These turbines can flush up to 200 tons of water per second into the Edo River—a rate fast enough to empty an Olympic-sized swimming pool in just 12 seconds. When dry, this eerie engineering wonder hosts public tours and cinematic film shoots.