It is the Godzilla of urban drainage schemes.

Tokyo has constructed a giant underground flood system at a cost of  $US2.6 billion to keep the city safe during typhoons and extreme rainfall events.

The G-Cans Project, or Metropolitan Area Outer Underground Discharge Channel, is comprised of huge tunnels, water tanks, pillars and pumps that work together to divert flood waters away from the mega-city and out to Tokyo Bay.

The project was undertaken by the Japanese Government and overseen by the Japan Institute of Wastewater Engineering Technology.

The tunnels run for more than 100km and there are 65m tall flow-regulating silos connected to them. The main tank is 25m tall and 177m long.

Check out the full article and more photos here: https://interestingengineering.com/tokyos-futuristic-underground-flood-system