In this video, a camera crew follows a city official to a trapdoor hidden in a Tokyo sidewalk, which opens to a narrow stairway leading to a giant underground warehouse stocked with emergency supplies. (Watch it.)
Located 20 meters (65 ft) underground, the 1,480 square meter (16,000 sq ft) space contains emergency supplies to be distributed to the public in the event of a major earthquake. Items include 5,000 blankets, 8,000 rugs, 4,000 candles, 300 cooking pots, 200 t-shirts, and emergency medical supplies. A conveyor belt system is installed to help transport the supplies up to street level.
The underground warehouse is connected to an unnamed station on the Oedo line, Tokyo's deepest subway. Apparently, the Tokyo Metropolitan Government maintains more than one of these warehouses, but the locations are kept secret.