Not for the claustrophobic, it takes about 10 minutes to walk through the Narusawa Hyōketsu (ice cave), formed by lava flows from an eruption of Mt Fuji in 864, to the end to see the ice pillars which are at their peak in April. A 20-minute walk down the road is the similar Fugaku Fukestu (wind cave, also known as the lava cave), which was used to store silk worm cocoons in the past.