Tokyo's Underground Cathedral protects against flooding

The Metropolitan Area Outer Underground Discharge Channel, often referred to as the ‘Underground Cathedral’, serves as a critical flood prevention system for Tokyo. Located in Saitama Prefecture, approximately 30 kilometers from the capital, the massive engineering project consists of concrete tunnels extending over 6 kilometers and reaching depths of 50 meters.

The structure features 59 massive columns, each weighing 500 tons, which support the ceiling and create a labyrinthine appearance. The system is designed to divert storm surge water through silos and underground tunnels into pressurized tanks before releasing it into the Edogawa River. This process occurs approximately seven times a year to prevent urban flooding.

Beyond its industrial utility, the site is a notable landmark used for film productions and video game design inspiration. The Japan National Tourism Organization (JNTO) notes that the facility is open to visitors, though tours require booking roughly one month in advance and necessitate safety equipment, including helmets and safety belts.