G-Cans Tunnel

The Metropolitan Area Outer Underground Discharge Channel , popularly known as G-Cans, is an underground water infrastructure project in Japan. It is the world's largest underground flood water diversion facility, built to mitigate overflowing of the city's major waterways and rivers during rain and typhoon seasons. It is located between Showa and Kasukabe in Saitama prefecture, on the outskirts of the city of Tokyo in the Greater Tokyo Area.