Japan Underground Flood Water Diversion

Gigantic Underworld

This is the world's largest underground flood chamber. Look at the people for scale. It's staggering. Pretty cool that you can visit it.

The Metropolitan Area Outer Underground Discharge Channel, popularly known as G-Cans, is an underground water infrastructure project located in Saitama prefecture on the outskirts of Tokyo, Japan.

It is built to mitigate the city's major waterways and rivers overflowing during rain and typhoon seasons.

The project started in 1992 and was completed by early 2006. So, 16 years of construction certainly makes this a mega project.

It consists of five concrete containment silos with heights of 65m and diameters of 32m, connected by 6.4km of tunnels 50m beneath the surface, as well as a large water tank with a height of 25m, with a length of 177m, with a width of 78m, and with fifty-nine massive pillars connected to 4x 10 MW (13,000 hp) pumps that can pump up to 200 metric tons of water into the Edo River per second.

This is seriously impressive civil and hydraulic engineering. If any of you have ever visited it, please let me know!