Ryūgū Dōketsu

Ryūgū Dōketsu is a lava and ice cave carved into Mount Fuji's northern slope, extending roughly 96 meters into the rock. Inside, temperatures remain between minus 2 and plus 3 degrees Celsius year-round, creating layers of permanent ice in the deeper chambers.

The cave formed thousands of years ago when flowing lava carved tunnels through Mount Fuji's rock during volcanic activity. It gained official protection as a natural monument in 1929, recognizing its geological value and enduring connection to local communities.

The main chamber holds the Senoumi Shrine, dedicated to the goddess Toyotama-hime no Mikoto, where visitors come to offer prayers. The sacred space blends religious devotion with the natural cave setting, creating a place where people connect with both earth and spirit.

The site is reachable via roads near Lake Saiko, making it fairly accessible to reach. Bring warm clothing since it stays cold inside year-round, and wear sturdy shoes because the cave floor is uneven and can be slippery.

Specialized spider species live in the cave's permanent freeze, adapted to survive in the icy depths. These rare creatures exist nowhere else and make the location a spot of biological intrigue for those who notice them.