Narusawa Ice Cave

All throughout the Aokigahara Forest are underground caves formed by lava from a massive eruption of Mt. Fuji in the year 864. Among them, the most common cave type is the lava tube: as lava cools from the outside in, the outer layers of the lava harden and form a roof and tunnel for the remaining lava to flow through. The resulting cavern is long and elongated, like a tube.

The Narusawa Ice Cave, located east of the Aokigahara Forest, is one such lava cave. It was formed around 1,150 years ago, and was designated a Natural Monument in 1929 by the Ministry of Education. The surrounding forest was a giant lake prior to Mt. Fuji’s eruption.

The 81-meter-long Narusawa Ice Cave forms a loop, inside which some of the tunnel sections have a ceiling just 90 centimeters high, forcing visitors to crouch or crawl through. The cave is covered in ice all year, and the temperature inside averages about 3°C. Water trickles and drips from the ceiling, forming ice pillars. The cavern was historically used as a natural refrigerator, before such machines were invented, and passing through it makes for a rejuvenating experience whatever the season.

Legend has it that the “Pit of Hell” in the deepest part of the ice cave is so long it leads all the way to Enoshima Island in Kanagawa Prefecture, though this is an unsubstantiated claim.