If the summer weather is too hot for you to go out exploring, check out this chilly Washington adventure. Not only is it cool, but it is also a pitch-black lava tube. We’re talking about Ape Cave, and here’s what to know about visiting.

Ape Cave is the third longest lava tube in North America, spanning 2.5 miles long, and is about nine miles east of Cougar, WA, within Mount St. Helens National Volcanic Monument.

The cave temperature is 42 degrees F year-round, so if you plan to visit, you will need warm clothes even in the warm weather. You will also want to wear sturdy shoes, and to bring two sources of light per person – note that cell phone lights are not bright enough for the caves!

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Image via USDA Forest Service

According to the USDA, “a short, paved, accessible trail beneath towering trees leads to a stairwell into the cave.

The one-way lower cave route is described as “relatively easy and family friendly.” They say to allow at least an hour to complete the 1.6-mile round trip.

For the more adventurous of visitors, there is a 1.5 mile upper cave route that travels over large rock piles and requires scaling of an 8-foot lava fall.

“Two-thirds of the way up you will pass beneath The Skylight, an opening to the surface. Do not try to climb out; this is NOT an exit. The upper entrance is only 0.25 mile ahead,” states the USDA. For this route, allow 2.5 hours for your hike.

To visit, there is a timed reservation system for the summer and through October 31. You can choose a two-hour time slot for your desired day.

When there, be sure not to touch cave walls or ceilings.

Ape Cave was discovered in 1947 by a logger named Lawrence Johnson, but it was not explored until the early 1950’s when a scout troop lowered a team of scouts down a 17-foot overhang to the cave floor, states the website.

Are you ready to explore it?

Ape Cave is located on Forest Road 8303. Timed reservations can be made here.

Ape Cave Interpretive Site

Where: Gifford Pinchot National Forest