The G-Cans project, also known as 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 Japan's severe monsoon seasons.

Begun in 1992, the two-billion-dollar project finally saw completion in 2009. The tunnels run over 100 kilometers, 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 commonly referred to 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, and, over the past decade or so, has proved useful for well over a hundred times. It has also become a popular filming location and been featured in numerous movies, TV series, and music videos. Join the official tour, and be awed by the massive Underground Temple in person.

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.