Fugaku Wind Cave

All throughout Aokigahara Forest are underground caves formed by lava from the massive eruption of Mount Fuji in 864 CE. 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 Fugaku Wind Cave is one such lava tube. It has an average internal temperature of 3°C, is 201 meters long and 8.7 meters high, and does not produce an audible echo. This is due to its porous basalt walls which help absorb sound.

The cave was formed around 1,100 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, and a dragon god was said to reside in it. This deity is still worshiped in the area, with its primary shrine located in the Ryugu Cave at nearby Lake Saiko.

Descending into the Fugaku Wind Cave, the visitor will encounter illuminated ice and impressive stalactites and ice pillars all along its length. During the Edo period (1603-1868), the cave was used as a natural refrigerator, and the ice cubes produced here were offered to local lords as tribute.

At the back of the cave are rock walls covered with schistostega pennata, a type of luminescent moss known as goblin gold or Dragon’s gold. It grows in damp, low-light conditions and has a greenish-gold glow.