Narusawa Hyoketsu Ice Cave
The Narusawa Hyoketsu Ice Cave is a steep passage leading 21 meters into the rock beneath the Aokigahara Jukai Forest. This geological curiosity is the result of a huge gas bubble in the lava flow that burst open just as the walls became cool enough to prevent collapse. Though many of the smaller shafts off the main cave remain unmapped, one particularly ominous abyss is known as the jigoku ana, or “hell hole.”
The cave consists of two stacked “rings.” The round-trip route from the surface through the rings is about 150 meters long and can be walked in 10 or 15 minutes. There are 91 stairs going down and 101 coming back up, and ice can make the path slippery. Visitors are encouraged to borrow a helmet at the entrance, as the ceiling is just 91 centimeters at its lowest point.
The depths of the Ice Cave remain at subfreezing temperatures all year. For ages, local residents evidently avoided it as a hazard, but from the early twentieth century it was used as a natural freezer to store ice and seeds. A shimmering “wall of ice” and frozen stalactites can still be seen along the route.