Overview
Ape Cave, deep in Gifford Pinchot National Forest near the southern Washington Cascades, is not a hiking trail in the conventional sense. There are no mountain views, no wildflowers, no rushing creeks. There is no daylight at all once you move 100 feet from the entrance. What Ape Cave offers instead is something genuinely rare: 2.5 miles of intact lava tube formed roughly 2,000 years ago by an ancient eruption of Mount St. Helens, accessible to the public and large enough to walk upright through much of its length.
The cave is divided into two sections with different characters. The Lower Cave (0.75 miles one-way) is the easy option: a flat, wide passage with moderate boulder-hopping, suitable for families and casual visitors who bring adequate lighting. The Upper Cave (1.5 miles one-way) is a different experience entirely: a route-finding challenge that requires climbing a 30-foot lava fall, squeezing through tight sections, and navigating uneven lava rock for over an hour without natural light.
Both sections share one absolute requirement: light. Not your phone flashlight. Proper headlamps (at least one per person, with backups). People have had to be rescued from this cave because their only light source failed. The cave is completely, totally dark without it.
Dogs are not permitted inside Ape Cave. This is a firm rule, not a suggestion. Leave your dog at home or with someone who can stay at the trailhead.
Getting to the Trailhead
From Portland, take I-5 north to Woodland (exit 21) and follow Highway 503 east. Continue through Cougar and turn left (north) onto Forest Road 90, then turn left onto Forest Road 8303 following signs for Ape Cave. The parking area is at the end of FR 8303, approximately 11 miles from Cougar. Total drive time from Portland is about 1 hour and 30 minutes.
From Seattle, take I-5 south to exit 21 (Woodland) and follow the same route east. Drive time from Seattle is approximately 2 hours and 45 minutes.
The parking lot is large and paved, with vault toilets and an interpretive kiosk. A Mount St. Helens National Volcanic Monument fee of $6 per person is required (or show an America the Beautiful Pass). This is separate from the Northwest Forest Pass. Fees are collected at a self-pay station at the parking area.
The lot fills on summer weekends, especially Saturdays in July and August. Arrive before 9 AM for reliable parking. Overflow parking is available along FR 8303 for a short walk.
What to Bring Before You Read Anything Else
- Two light sources per person. Headlamps (not phone flashlights) are the standard. Bring a primary headlamp and a backup, even if that backup is a small flashlight in your pocket. Do not enter this cave with one light source. Batteries fail. Bulbs fail.
- Warm layers. The cave is 42 degrees F year-round, without exception. In a t-shirt, you'll be shivering within 15 minutes. In summer heat, people step into the cave underdressed and immediately regret it. Bring a fleece or jacket minimum; a hat and gloves make the Upper Cave comfortable.
- Sturdy footwear with ankle support. The lava rock floor is uneven, angular, and punishing on ankles. Trail runners work for confident hikers; hiking boots are better.
Lanterns are available for rent at the Ape's Headquarters building adjacent to the cave entrance, for approximately $5. They're worth it as a supplemental light source, especially for the Lower Cave. The rental station is open seasonally (typically May through October) during daylight hours.
The Route
Lower Cave (0.0 to 0.75 miles one-way)
The cave entrance is a collapse pit: a hole in the ground roughly 20 feet across, reached by a short path from the parking lot. A staircase descends about 30 feet into the tube. At the bottom, the cave stretches in two directions. Turn right for the Lower Cave.
The Lower Cave passage runs 0.75 miles south to a collapsed lava tube exit called the "lower entrance," which is closed (the passage is blocked by collapsed rock). In practice, you walk 0.75 miles in, stop, and walk back. The passage is wide (sometimes 20 to 30 feet across) and mostly flat, requiring some boulder-hopping over piles of breakdown rock but no technical moves.
Notable features along the Lower Cave:
At about 0.3 miles, the passage narrows and the ceiling drops. Tall hikers will duck. Shortly after, the tube opens into a large room before closing again.
At 0.5 miles, look for the "lava balls" on the floor: rounded chunks of hardened lava that dripped from the ceiling while the lava was still flowing and bounced across the tube floor as they cooled. They look like oversized cannonballs and range from softball-sized to 2 feet across.
At the far end of the lower passage, the ceiling comes down and the cave effectively ends in a breakdown pile. Turn around here.
Total time for the Lower Cave out and back: 45 minutes to 1.5 hours depending on pace and how long you stop to look around.
Upper Cave (0.0 to 1.5 miles one-way)
From the main entrance staircase, turn left for the Upper Cave. This section is the longer and harder of the two, running 1.5 miles north and emerging at a surface opening called the "upper entrance" (often called the "skylight"). A short trail on the surface connects the upper entrance back to the main parking area, making the Upper Cave a one-way through-hike if you prefer.
The first 0.5 miles of the Upper Cave is wide and relatively straightforward, similar in character to the Lower Cave. Then the passage gets serious.
The Lava Fall: at approximately 0.5 miles, the tube floor rises abruptly by 8 feet at a ledge, then again at a 30-foot wall of hardened lava. This lava fall requires climbing: hands on the rock, feet finding footholds, body moving up the face. It is not technical climbing, but it requires both hands and a willingness to commit to the moves. People in sandals or carrying small children will struggle here. If you're not comfortable with this type of movement, the Lower Cave is the better choice.
Above the lava fall, the tube continues north. The floor becomes increasingly uneven and the passage narrows in places. At roughly 1.0 mile, look for the "Meatball": a large lava ball, approximately 18 inches across, wedged in a crack above the passage. It has been suspended there for 2,000 years.
The passage ends at the upper entrance, a skylight in the cave roof where daylight streams in. A ladder leads up through the opening to the surface. From here, a marked trail on the surface (about 0.25 miles) leads back to the main parking area.
Total time for the Upper Cave one-way (including the surface return): 2 to 3 hours.
Permit Requirements
There is no permit or reservation required for Ape Cave itself. The Mount St. Helens National Volcanic Monument fee ($6 per person) is required and covers entry for all sites within the monument that day. America the Beautiful annual passes (National Parks and Federal Recreational Lands passes) are accepted and cover the fee for the pass holder plus three additional adults.
The fee is separate from any Northwest Forest Pass you may have. A Northwest Forest Pass alone does not cover the monument entry fee.
When to Hike
Ape Cave is accessible year-round, which makes it genuinely unique among Pacific Northwest outdoor destinations.
Summer (June through September): The most popular period. The contrast between the summer heat outside and the 42-degree cave makes this especially appealing in July and August. The parking lot is the most crowded during this window. Arrive early or accept competition for spaces.
Fall (October and November): Excellent timing. Crowds thin dramatically after Labor Day. The weather above ground is cooler, which makes the temperature difference less jarring, and fall color surrounds the trailhead.
Winter (December through March): The cave remains at 42 degrees and accessible for those willing to make the trip. The road to the trailhead is plowed and remains open (unlike most higher-elevation Gifford Pinchot roads). In heavy snow years, snowshoeing from the gate to the trailhead adds a mile or two. Check current road conditions through the Mount St. Helens Institute before visiting.
Spring (April and May): Good conditions. The cave is the same regardless of what's happening outside, and spring means the lot is quieter than summer. Early April can still have snow on the access roads; check before driving.
What to Bring
- Two headlamps per person (required): Bring extra batteries if your headlamps take them.
- Warm jacket or fleece: 42 degrees F feels genuinely cold when you're standing still in the dark. Bring more than you think you need.
- Hat and gloves (optional but appreciated): Especially for the Upper Cave where you'll be spending more time stationary on the lava fall.
- Sturdy shoes or hiking boots: The lava floor is the roughest terrain on this list. Sandals are a recipe for twisted ankles.
- Snacks and water: You won't be hiking far, but you'll be in a cold environment. A hot drink in a thermos is a legitimate quality-of-life upgrade in winter.
- Camera: Long-exposure photos in a lava tube look extraordinary. A tripod and a willingness to experiment are worthwhile.
Trailhead Access
The Ape Cave parking area has vault toilets but no running water or concessions beyond the lantern rental station (seasonal). The nearest services are in Cougar, WA (about 11 miles west on Highway 503), which has a small store and gas.
Lava Canyon Trail is approximately 20 miles east on Forest Road 83, making a natural pairing for a full volcanic geology day. Do the Lower Cave at Ape Cave in the morning (about 1.5 hours), then drive to Lava Canyon for the afternoon.
The Mount St. Helens Visitor Center at Silver Lake (off I-5, exit 49) provides the full eruption history and context if you want background before visiting the cave. The Johnston Ridge Observatory (north side of the volcano) is open seasonally and provides the most dramatic views of the 1980 crater.
If you're spending a full weekend in southern Washington, Norway Pass on the north side of Mount St. Helens gives you a surface-level look at the 1980 blast zone to pair with the underground perspective at Ape Cave. The Lewis River Falls Trail is another excellent option, about 30 minutes south of Ape Cave on Forest Road 90, with three major waterfalls in a single old-growth corridor.
Ape Cave fills a gap in the outdoor experience inventory: it's a place where you can go when smoke blocks the mountain views, when rain makes ridge hiking unpleasant, or when the kids need something different. It is also, on its own terms, one of the most unusual geological features you can walk through in the continental United States. For a broader comparison of how national forests make these kinds of geological features accessible, see national forest vs. national park.