Ape Cave is a lava tube located in Gifford Pinchot National Forest just to the south of Mount St. Helens in Washington state. Its passageway is the longest continuous lava tube in the continental United States and the third longest (in total mapped length) lava tube in the North America at 2.5 miles (4,023 meters). Ape Cave is a popular hiking destination with beautiful views of the Mount St. Helens lahar region.