Step beneath the forest floor and discover one of the most unique adventures in the Mount St. Helens region. Ape Cave is a massive lava tube formed by ancient volcanic flows on the south side of Mount St. Helens, and at about 2.5 miles long, it is considered the third longest lava tube in North America. This unforgettable stop blends geology, adventure, and forest scenery into one of the area’s most memorable outdoor experiences.
The experience begins with a short paved path from the parking area to the cave entrance, where a stairway drops into a cool, dark underground world. From there, visitors can choose between two very different routes. The Lower Cave is the easier option, offering a relatively gentle out-and-back walk that is well suited for families and casual explorers. The Upper Cave is more challenging, with rocky footing, lava-formed obstacles, an 8-foot lava fall, and an exit ladder that brings you back to the surface for a forest hike to return to the main entrance.
Ape Cave is more than a hike. It is a chance to experience Mount St. Helens from the inside out. The cave stays around 42 degrees year-round, making it a refreshing summer adventure but one that requires preparation in every season. Visitors should bring warm layers and at least two reliable light sources per person, since there is no lighting inside the cave and cell phone flashlights are not considered adequate.
To help protect this fragile volcanic environment, visitors should avoid touching the cave walls or ceiling, and pets, smoking, camping, alcohol, and food or drinks other than water are not allowed inside. During the open season, timed entry reservations are required per vehicle, and parking also requires a Northwest Forest Pass, Interagency Pass, or day pass.
Whether you are looking for a family-friendly lava tube walk or a more adventurous underground scramble, Ape Cave offers a one-of-a-kind way to explore the volcanic story of Mount St. Helens. It is one of those places that feels equal parts trail, cave, and natural wonder.
Trail details: Ape Cave Trail #239, near Cougar, Washington. Main trailhead coordinates: 46.108645, -122.210387. The cave is reached via Forest Road 8303, roughly 9 miles east of Cougar.
Call to action: Add Ape Cave to your Mount St. Helens itinerary and experience one of the most unusual hikes in Washington, where volcanic history comes to life beneath your feet.
Current seasonal note: As of April 8, 2026, Ape Cave is in its winter closure period. The Forest Service page lists the site as seasonally closed from November 1 to May 17, while Recreation.gov currently says the 2026 summer season reopens on Friday, May 22 and requires timed tickets.