Ape Cave is a lava tube located in Gifford Pinchot National Forest just to the south of Mount St. Helens in Washington state, discovered circa 1951. Its passageway is the longest continuous lava tube in the continental United States and the third longest (in total mapped length) lava tube in North America at 2.5 miles (4,023 meters). Ape Cave Trail No. 239, which runs along the interior of the cave, is a National Recreation Trail receiving 170,000 visitors each year.