All throughout Aokigahara, a forest on the island of Honshu in Japan, are underground caves that were formed by volcanic activity from the nearby Mount Fuji. If you ever go exploring, you may just fall into one. One of the largest and most impressive of these lava caves is the Narusawa Hyoketsu.

Stairs lead down into the 70-foot-deep cavern and areas where you must crouch to get through. Once you reach the bottom, the ice is crystal clear and stunning, catching the color-changing light beautifully.

Narusawa Hyoketsu formed as a result of a massive eruption of Mount Fuji in the year 864. Lava flowed through a channel beneath the hardened surface, leaving behind this 156-meter (512-foot) underground tunnel. The average temperature of the cave is around zero degrees Celsius. As water drips through the rock, it freezes into long, spindly icicles as well as larger pillars of ice, some of which stand around 30 meters (100 feet) tall.

The ice is there year-round, though it is larger in the winter, when icicles can reach up to three feet long.  Located on the edge of the Aokigahara, also known as the "Sea of Trees," Narusawa Hyoketsu is designated a Natural Monument of Japan.