The Metropolitan Outer Area Underground Discharge Channel is an underground waterway that connects 5 medium-sized rivers flowing through Saitama prefecture, in order to divert flood water to Edo river to prevent floods. It is a tunnel 50m beneath the ground and 6.3km long. A part of in went into service in 2002, and the remaining part in 2006.
A part of the eastern end of the Metropolitan Outer Area Underground Discharge Channel, around the Shōwa Drainage Pump Station, is open to the public as The tour of the Metropolitan Outer Area Underground Discharge Channel, and the the huge Pressure-adjusting Water Tank, often refered to as the "Underground shrine", can be seen.
Paricipating on a tour of the "Underground shrine".