The G-Cans project (Shutoken Gaikaku Housui Ro, or the Metropolitan Area Outer Underground Discharge Channel) is a massive underground waterway and water storage area built by the Japanese government to protect Tokyo from flooding during the monsoon seasons.

Begun in 1992, the two-billion-dollar project was completed in 2009. The tunnels run over 100 km, but perhaps the most impressive features of the drainage system are the 213-foot-tall silos and the 83-foot-tall, 580-foot-long pillared main tank known as the “Underground Temple,” which was built to collect run-off from the city’s waterways. The humongous drainage system can pump over 200 tons of water a second.

A free tour is offered in Japanese only. It is requested that you bring along a translator for “safety reasons.”

Explorer of Japanese ruins Michael John Grist will be leading an Obscura Day expedition to the G-Cans project, a massive underground waterway and water storage area built by the Japanese government to protect Tokyo from flooding during the monsoon seasons.