Ape Cave Lava Tube in Mount Saint Helens National Volcanic Monument

Do you want to go on a long hike in a dark tunnel? Ape Cave is the place. Ape Cave is one of the longest lava tubes in the world, measuring approximately 2.5 miles from end to end. Hikers may travel unguided through the lava tube. Make just a few preparations and Ape Cave will deliver a one-of-a-kind adventure.

From the cave’s main entrance, visitors have two options:

• Head down to the lower end and back for a 3/4 of a mile round trip hike
• Trek up the cave 1.5 miles to an upper entrance, gaining 400 feet over numerous dark obstacles. Resurface and return to the main entrance by hiking back 1.25 miles above ground. The mile and a half underground takes approximately two hours to complete, but the memory will last a lot longer.

Before setting out, be sure that you have at least three sources of light per person. A bright lantern is a very useful, as the black walls of volcanic rock aggressively absorb the light from flashlights. Several breakdowns are located in the cave, where rocks from the ceiling of the tube have crashed to the floor creating piles of jagged boulders that you must traverse. As a result, sturdy footwear is a must.

The temperature in the cave hovers in the lower 40s. You will encounter strong breezes in narrow stretches of the tube that can chill things even further, so dress accordingly.

A white moisture covers some walls of the cave, which visitors have unfortunately written on with their fingers. Do not touch the “cave slime” as it takes years for this fungus to regrow. Other commonsense rules include: no food or beverages, no smoking, no fires, no rock collecting, no littering, and no pets.

How was this incredible cave formed?

Approximately 2,000 years ago, Mount Saint Helens had an eruption of red flowing lava, an incredibly rare type of eruption for volcanoes in the Cascade Mountains. (Mount Saint Helens explosive eruption in 1980 is a good example of how volcanoes in this range typically erupt.) This flow of basalt (liquid lava) burned down the south slope of Mount Saint Helens into a stream bed. The surface cooled and hardened, insulating the lava underneath, which continued to flow, eroding away rocks and soil. After months of lava flow, the volcano went dormant. The remaining basalt flowed until it hardened, leaving an empty tube behind.

The cave went undiscovered until 1947, when a logger nearly lost a tractor in the sinkhole that is now the cave’s main entrance. A local club nicknamed the Helens Apes first explored the cave, giving the tube its name.

Descend the metal staircase into Ape Cave and enter a world of darkness. The lower stretch of the cave takes about an hour to explore. In this area you will see a formation called “the meatball,” where a round block of lava fell from the ceiling into flowing lava and was carried to an narrower section where it became wedged.

Traveling up the lava tube provides a longer and more difficult hike. Some of the hiking is easy, unobstructed walking over a smooth floor. However, two dozen breakdowns complicate the path, requiring you to climb over piles of ceiling fragments. Additionally there are choke stones to crawl under and dry falls to climb up, including one vertical dry falls that is 8-feet tall. It is pitch black in the cave, making it easy to lose track of time and distance. The good thing is, you can’t get lost. The cave has not junctions, so just head up the tube.

The ceiling of Ape Cave is high, approximately 50 feet in areas. The “big room” of the tube is 88-feet wide, while narrower passages are just a few feet wide.

After what feels like hours walking in the dark, you will start to imagine that there is light ahead in the tube. As you get closer, you discover that it wasn’t your imagination. Light really is coming in from a skylight overhead. Alas, the first skylight you reach is not the cave exit. Luckily, a second skylight is not far beyond with a metal ladder that will bring you back to the surface.

Let the sun’s rays warm you up as you hike 1.25 miles on an easy downhill grade back to the main entrance of the cave and on to the parking lot.

Ape Cave Lava Tube is located in Mount Saint Helens National Volcanic Monument in Gifford Pinchot National Forest. A Northwest Forest Pass is required to park at the trailhead. You may self-register for the $5 day pass at the trailhead. An annual America the Beautiful national parks pass can also be used in lieu of the regional national forest pass. To crawl through a smaller lava tube and learn more about volcanoes, visit nearby Trail of Two Forests. For another long hike through a lava tube, check out Lava River Cave near Bend, Oregon.

To get to the trailhead: From Interstate 5, 140 miles south of Seattle and 25 miles north of Portland, take exit 21 on to Route 503 East toward Cougar. After 35 miles, turn left on Forest Service Road 83 and drive two miles north to Forest Service Road 8303. Turn left again and drive 0.9 miles to the trailhead parking area on the right after the Trail of Two Forests.

Trailhead address: National Forest Road 8303, Gifford Pinchot National Forest, Cougar, WA 98616
Trailhead coordinates: 46.108362, -122.211432 (46° 06′ 30.10″N 122° 12′ 41.15″W)