A worker standing inside the underground water tank. Floodwater is stored here, before it is pumped into the Edo River. Photo: CHARLY TRIBALLEAU/AFP via Getty Images
This tank has 59 pillars, each weighing 500 tons. Photo: Chris McGrath/Getty Images
The flood prevention system's tanks, over 72 meters deep, are big enough to hold a space shuttle. Photo: CHARLY TRIBALLEAU/AFP via Getty Images
Tourists entering the underground water tank. Photo: Chris McGrath/Getty Images
Visitors can tour the floodway during dry season. Photo: Chris McGrath/Getty Images
