Ape Cave is a lava tube located south of Mount St. Helens in Washington’s Gifford Pinchot National Forest. Ape Cave was formed by a lava flow from Mount St. Helens about 1,900 years ago. It is the 2nd longest lava tube in the continental United States after nearby Deadhorse Cave.

Ape Cave is not developed like a show cave, but there are 2 cave tours and a surface trail with interpretive signs. The trail through the lower cave takes about an hour. The lower cave is a fairly level and the floor is covered by mudflow, which is easy to walk on. The highlight is the Lava Ball formation in the ceiling.

In the upper cave it is necessary to climb over large rock piles. The most difficult spot is a 2.40m high lava fall. The cave visit is completed by an interpretative trail above ground, called Ape Cave Trail.