Halloween seems the right time to delve into the subject of spooky caves and where to find them around Western Washington. Here's a primer on the Ape Cave at Mount St. Helens, Boulder Cave on the Chinook Pass Highway, and the Bat Caves of Blanchard Mountain.

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It’s Halloween, the season of the spooky, the scary, the eerie, the weird. In honor of this, we thought we’d explore some deep, dark mysterious spots that offer opportunities for spine-chilling outdoor adventures. (Diabolical laughter goes here.)

Places with names like … Ape Cave! … Bat Caves! … Boulder Cave! … The Meatball! (OK, maybe that last one’s not so scary.)

Ape Cave

Located on the south side of Mount St. Helens, about 3 ½ hours from Seattle, Ape Cave is the longest continuous lava tube in the Lower 48. It formed about 2,000 years ago when lava flowed down a streambed, hardening on the edges while continuing to flow down the center; thus a tube was born.

It takes its name from a 1950s outdoors group (or Boy Scout troop, depending on whom you ask) that used to explore the area and who referred to themselves as “The Mount St. Helens Apes” (this is, after all, Sasquatch country).

Highly popular with summer visitors, Ape Cave is also open year-round and makes for a unique fall and winter destination, when you might find subterranean solitude. Do be aware that the Ape’s Headquarters — where many summer visitors rent lanterns — is closed for the season and that it’s imperative to bring your own light source.

“It’s completely dark inside so we recommend a headlamp and a Coleman-type lantern,” says Diane Tharp, a spokeswoman at Mount St. Helens’ National Volcanic Monument Headquarters.

“Headlamps are great because in the upper cave, you’ve got places where you’re climbing up over the lava boulders, and so it’s nice to have your hands free.”

Though really just one continuous 2-mile underground lava tube, Ape Cave has two entrances; thus, a lower and upper cave. The lower cave is a relatively flat 0.8 miles (one-way) and smooth, and varies in height (up to 20 feet) and width (to 40 feet). Near its southern end is the aforementioned Meatball, formed when a fragment of rock fell from the roof during cave formation — thus getting covered in lava — and today resembling a mega meatball.

The route through the upper cave is a bit more challenging. Along with gaining 365 feet of elevation over its 1.2 miles (one-way), the cave twists and winds and requires a bit of hands-and-feet scrambling up steep pitches.

“We highly recommend leather gloves in the cave because when you’re climbing over the boulders they can be very rough,” Tharp says.

Something else that’s pretty cool is that offseason visitors could conceivably visit the cave to warm up. Since the inside is perpetually 42 degrees Fahrenheit, summer visitors often feel like they’ve stepped into a refrigerator. But when late fall and winter temps dip down to the 20s, the cave’s 42 could feel balmy. Sorta.

IF YOU GO: Take Interstate 5 to Exit 21 at Woodland, Cowlitz County, then head east on Highway 503 toward Cougar. Seven miles east of Cougar (now on Forest Road 90), turn left on Forest Road 83. In 2 miles turn left onto Forest Road 8303. Park at the Trail of Two Forests parking lot 0.2 miles ahead; it’s about a mile walk (or snowshoe, in winter) to the Ape Cave. (The Ape Cave parking lot is closed for the season.) Northwest Forest Pass required; Sno-Park permit required after Dec. 15 at Trail of Two Forests lot.

MORE INFO: Mount St. Helens National Volcanic Monument, 360-449-7800 or fs.usda.gov/mountsthelens.

Boulder Cave

Though closed from Oct. 1 until April 1 to protect a small population of Townsend big-eared bats who winter here, this 475-foot-long tunnel is definitely worth putting on next year’s outdoor adventure punch list.

Located off Highway 410, about 26 miles east of Chinook Pass, the cave was formed by water erosion — Devils Creek still flows through the cave — and as such, is one of the largest of its kind. It’s accessed via a gently inclining 0.7-mile trail through Ponderosa pine woods, with nice views along the way into the deeply notched, narrow chasm carved by the creek as it continues downhill from the cave.

A few decades ago, several thousand bats called this cave their home, but over time that population has dwindled to just a few dozen. So as to not disturb the bats, cave visitors are advised to whisper if they must talk and to direct flashlight beams only on the trail and not the cave walls.

A more recent concern is that of white-nose syndrome (WNS), a fungus afflicting bats in caves in the Eastern U.S. that forms on bats’ muzzles and has been associated with more than a million bat deaths. Discovered in 2006, as of yet, WNS hasn’t made its way to Washington but concerns are that if it does, it could easily wipe out the Boulder Cave bat population, so signs discourage visitors who’ve recently visited other caves from wearing the same shoes, clothing, etc.

IF YOU GO: When conditions permit, take Highway 410 east over Chinook Pass (usually open late May to mid-November) and continue for 26 miles. Just before Cliffdell, turn right onto a road signed “Boulder Cave National Recreational Trail.” Cross the Naches River and just ahead turn right onto Forest Road 1704 (Old River Road). The trailhead is 1.1 miles ahead. Northwest Forest Pass required.

MORE INFO: Call the Naches Ranger District at 509-653-1400 or see www.nachesvalleychamber.com/info/bouldercave.html.

Bat Caves

With a name like Bat Caves, these Blanchard Mountain (Skagit County) holes sound just about perfect for Halloween exploration. Except they’re not really caves, but rather, deep, dark crevices between the rocks in a boulder field at the base of a 300-foot rock wall, the Oyster Dome. Whether or not bats actually still hang out down in those crevices (albeit, upside down) seems to be open to debate. But what’s not, however, is the absolute “wow!” factor of the hike to get there — it’s off the charts!

The Oyster Dome trail (3 miles one-way) offers stunning views of water, the San Juan Islands and Olympic Mountains, especially from the 2,085-foot top of the dome. About 2.5 miles along the trail, the short Talus trail leads a couple hundred yards to the Bat Caves which, with their jumble of large, somewhat flat boulders, make for a great picnic spot.

The caves (that is, crevices) themselves are better left unexplored. A nearby sign warns those considering an exploration to watch out for cold water-induced fatigue, skunk dens, speleophobia, animal or human feces, toxic calcium carbide and more.

IF YOU GO: Head north on Interstate 5 to Exit 231 in Burlington. Go north on Chuckanut Drive (Highway 11) for about 10 miles. Roadside parking is on the west side of the road, just past Milepost 10.

Mike McQuaide is a Bellingham freelance writer and author of “Day Hike! Central Cascades” (Sasquatch Books). He can be reached at mikemcquaide@comcast.net

. His blog is mcqview.blogspot.com.