Narusawa Ice Cave, Yamanashi

A lava tube formed by an eruption of Mount Fuji. Even in summer it averages about 3°C inside, and columns of ice line the cave.

Blocks of ice lit in blue under a rough lava ceiling in Narusawa Ice Cave — Photo: Osumi Akari, CC BY-SA 4.0, via Wikimedia Commons

Stone steps and railings leading down to the entrance of Narusawa Ice Cave in the forest — Photo: Kounoichi, CC BY-SA 4.0, via Wikimedia Commons

A cave made by an eruption over 1,100 years ago

Narusawa Ice Cave is a lava cave in Narusawa Village, Yamanashi Prefecture, inside Aokigahara Jukai (a vast forest that grew on top of lava) at the foot of Mount Fuji.

It is a tunnel that formed inside hot, flowing lava when Mount Nagao, a parasitic cone of Mount Fuji (a small volcano on the flank or at the foot of a larger one), erupted in 864 (the 6th year of the Jogan era). It was designated a national Natural Monument in 1929.

A loop-shaped cave with ice all year round

The cave forms a ring and is 153 m long in total. The average temperature inside is about 3°C, and there is ice to see throughout the year.

The ice pillars, formed as water seeping from the ceiling freezes, grow from winter into spring and are at their best around April. The biggest reach about 50 cm across and about 3 m tall. The route loops round and back to the exit, taking you past rough, bumpy lava walls and ceilings.

Watch out for the low ceiling and the stairs

The ceiling is low throughout, only about 91 cm at its lowest, and in places you have to crouch to get through. The stone steps are wet and slippery, and even more so in spring because of the ice. On the way out there is a flight of stairs climbing 21 m in one go.

Because some parts are narrow and hazardous, children under 100 cm tall are not allowed in, and you cannot carry a child in on your back or in your arms either. Pets are not allowed, even in a carrier.

Getting there

It is about 30 minutes by bus from Kawaguchiko Station on the Fujikyu Line. About 800 m to the west is another lava cave, Fugaku Wind Cave, covered on the same official website, and you can visit both.

Opening hours vary with the season and conditions inside the cave, and there is a closed period in December. Check the official website before you go. At busy times, a mobile ticket lets you skip the queue at the ticket window.

Tips

Even in midsummer it is as cold as winter inside the cave. Bring an extra layer.
High heels are dangerous. Wear comfortable shoes with good grip.
It can be enjoyed on rainy days too, so it is a good choice when the weather turns around Lake Kawaguchi.