With a total length of more than 2 miles, Ape Cave is the longest lava tube in the continental United States. Located on the south side of Mount St. Helens, the site offers routes through both the upper and lower tubes of Ape Cave. Both tubes remain a constant 42 degrees Fahrenheit throughout the year.
You will find an ample amount of informational and educational signs at the trailhead, at the mouth of the cave, and along the forest trail, all of which directs you to the cave of your choosing and back to your car. The easier of the two choices, the lower tube, is less than a mile long and can be hiked down and back in approximately one hour. The upper Ape Cave is 1 1/2 miles long and will take more than two hours to complete, which includes returning to the parking lot via an above-ground trail. The upper tube is clearly a more adventurous route, as this section of the cave requires scrambles over a number of boulder piles and ducking through some tight passages.
Ape Cave is open year-round, although winter access may require a hike in with snowshoes. No matter what the weather conditions are outside, the caves will always be a damp-and-dark 42 degrees, so be sure to bring warm clothing as well as a headlamp and/or flashlight with backup batteries.