You are looking at the world’s largest underground flood water diversion facility. The Metropolitan Area Outer Underground Discharge Channel, also known as the G-Cans Project, is an underground water infrastructure project in Kasukabe, Saitama, Japan. It was built to prevent overflow of the city’s major waterways and rivers during heavy rain and typhoon seasons. Work on the project started in 1992 and was completed by early 2009. It consists of five concrete containment silos with heights of 65 m (213 ft) and diameters of 32 m (104 ft). It is connected by 6.4 km (4 miles) of tunnels, 50 m (164 ft) beneath the surface. There is also a large water tank (shown above) with a height of 25.4 m (83 ft), a length of 177 m (581 ft), and a width of 78 m (256 ft). There are 59 massive pillars connected to a number of 10 MW pumps that can pump up to 200 tons of water into the Edogawa River per second.