Narusawa Ice Cave, Lava tube in Narusawa, Japan

Narusawa Ice Cave is a lava tube in Aokigahara forest, Narusawa Village, Yamanashi Prefecture. It runs 156 meters with two lobes, 1.5–11 meters wide and 1–3.6 meters high, and has a vertical shaft ring shape. Inside, the temperature averages about 3°C; at the 21-meter-deep Wood Pool, ice pillars and basalt lava formations are visible. Some ceilings are low enough that visitors must crouch.

The cave formed during the Jōgan eruption of Mount Fuji in 864, when lava cooled and trapped gases escaped, leaving a hollow tube. It was designated a Natural Monument of Japan on 17 December 1929. During the Edo period ice cut here was sent to the shōgun in Edo, and in the early 1900s the ice was used in refrigerators before electric models arrived.

The cave's name, Narusawa Hyōketsu, combines the village name with the word for ice cave. During the Edo period, ice cut here was sent to the shōgun and his entourage in Edo. In the early 1900s, ice from the cave was used in refrigerators before electric models arrived.

The cave is reached by a driveway off National Route 139 into the Aokigahara forest, next to the Fugaku Wind Cave; buses run from Kawaguchiko Station, about 25 minutes, and by car it is roughly 15 minutes from the Kawaguchiko interchange. Inside, the year-round average is about 3°C, and some sections have ceilings so low that visitors must crouch to pass.

The cave's shape is a vertical ring, tateana kanjōkei, so the visitor route loops down and back up rather than running straight through. The lowest point is Kinoike, the Tree Pool, 21 metres down, where ice pillars stand among basalt lava blocks. The cave lies in the Aokigahara forest, reached by a road off National Route 139.