Funatsu-Tainai Lava Tree Mold in Fujikawaguchiko, Japan

At the base of Japan’s Mount Fuji, there is a fascinating cave with several stories to tell. Located by the Kawaguchiko Field Center and part of the Mount Fuji World Heritage Site, the Funatsu-Tainai lava tree mold is one of the smaller and quieter caves of the Kawaguchiko area. The straight and narrow shape of this cave is due to a process known as lava tree molding. In the year 937, eruptions from Mount Fuji created the Ken-Marubi lava flow on the mountain’s northern slopes, engulfing a series of fallen trees. While the lava cooled around them, the trees were burnt away, leaving a uniform tube in the ground. The undulating inner surface of the cave, caused by the burning trees, is reminiscent of a human womb.

When adherents of the Fuji-ko folk religion found this cave, the womb-like appearance was not lost on them. They believed that entering and exiting the womb of Mount Fuji was a type of spiritual rebirth, and they could then be pure as babies before climbing the mountain. Expecting mothers would visit the cave as well, to pray for a safe delivery. Legend tells that the goddess Konohanasakuya-hime, patron of Mount Fuji, once gave birth here.

Today, the entrance to the cave is marked by a shrine to Konohanasakuya-hime. The goddess has had several of her shrines burned over the centuries by eruptions from the mountain. While the volcano is still active to this day, the last confirmed eruption was over 300 years ago. Today, the cave is open to all visitors.