G-Cans in Japan - Tokyo Metropolitan Outer Underground Discharge Channel

Coming up first is a holiday to Japan with a visit to the world famous G-Cans! (More information here and here; with more pictures here.) In Japanese this is called the 首都圏外郭放水路 shutoken gaikaku hōsuiro, and it's a massive underground system of interconnecting tunnels and basins for excess water. To walk around inside this structure is going to leave a lasting expression to be sure.