About Ape Cave
Ape Cave is a tunnel formed not by miners or underground rivers, but by flowing lava. The tube runs roughly two and a half miles beneath the forest south of Mount St. Helens and is one of the longest lava tubes in North America.
The cave formed around two thousand years ago when the outer surface of a lava flow cooled and hardened while molten rock continued moving beneath it. After the flow drained away, the hardened shell remained as a long underground passage.
Exploring Ape Cave is very different from walking through a brightly illuminated commercial cavern. Visitors need their own reliable lights, sturdy footwear, and cold-weather clothing. The easier lower route follows a relatively accessible portion of the tube, while the upper route includes rock piles, rough terrain, and an approximately eight-foot lava fall that requires scrambling.
Timed parking reservations are required during the managed season, and conditions should be checked before visiting. Above ground, the forest gives little indication that a miles-long volcanic tunnel runs underneath it. Once inside, the ordinary Washington woods are replaced by black basalt and complete darkness.