The G-Cans Project (formally known as the Metropolitan Area Outer Underground Discharge Channel) is the world's largest flood water drain facility located 50 meters below ground in the outskirts of Tokyo, Japan. Built between 1992 and 2009, the massive underground tunnel system is equipped with four jet-powered turbines and five gargantuan water silos that can drain floodwaters at an impressive rate of a 25-meter swimming pool per second.