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Carlsbad Caverns, NM
If claustrophobia has been deterring you from caving, pay a visit to the Big Room in Carlsbad Caverns National Park. The room, more like a cathedral, is 4,000 feet long and over 250 feet tall. Accessible by elevator as well as on foot, this might be the perfect place to ease yourself into spelunking. If you like what you see—scenic forests of stalactites hanging from the ceiling and otherworldly hoodoos poking up from the floor—you can take slightly more adventurous guided ranger tours further into the narrower portions of the cavern system. A bonus to visiting in any season other than winter is the nightly sight of thousands of Mexican free-tailed bats leaving their daytime roosts and heading out to catch flies in the New Mexico dusk.
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Kartchner Caverns, AZ
About an hour’s drive from Tucson lies Arizona’s other grand hole in the ground, the cave system at Kartchner Caverns State Park. The caverns weren’t discovered until 1974, and have been exceptionally well preserved since then. Tours of the Big Room include viewings of particularly unusual and vividly colored formations, including quartz needles, stalactites over 20 feet long, and the world’s largest trove of brushite moonmilk—that’s a mineral formed when bat guano meets calcite and clay, and it’s a lot cooler looking than it sounds. No independent exploration is allowed at Kartchner Caverns, but on Saturdays rangers lead headlamp tours, where you experience the cave the way the caverns’ discoverers did—by the glow of your own single light.
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Sea Lion Caves, OR
Just off Highway 101 about halfway up the Oregon Coast is America’s largest sea cave, part of a cluster of adjoining caverns known simply as the Sea Lion Caves. The two-acre, 125-foot high main cavern is indeed a year-round home to populations of both Steller’s and California sea lions. Take an elevator down into the scenic cave, which, even if it happens to be empty of large marine creatures, is still a spectacular sight with its red and green mineral- and lichen-streaked walls. The pinnipeds aren’t the only wildlife you’re likely to see—the rocky ledges in front of the caves attract sea birds like puffins and plovers. Venture out onto the deck next to the gift shop at road level and you might be rewarded with glimpses of migrating gray whales and orcas.
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Crystal Cave, CA
It’s located a good hour from the Sequoia National Park visitor center, and it’s only open from late May until the end of September, but the Crystal Cave is well worth the trip. A variety of tours introduce you to the maze of marble passageways in as tame or as wild a fashion as you desire. Follow a guide a half-mile or so along paved paths to view delicate mineral formations. Or book a wild cave tour where you’ll still be chaperoned, but you’ll have the chance to crawl around and get dirty in more labyrinthine parts of the cave system where there are no paths and no lights other than your headlamp.
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Oregon Caves National Monument, OR
As with most caves open to the public, the exploration experience at Oregon Caves National Monument & Preserve is guided. But this one feels more adventurous than some, as it’s a fairly rugged guided hike, with quite a bit of elevation gain, and some long, low passageways where you’ll definitely have to put away the selfie stick. In addition, while all caves are cool, this one, 220 feet below the ground, stays a downright chilly 44 degrees. To get a feel for what it was like to be one of the first people to explore the huge marble room, book a candlelight cave tour (it’s the last one of the day). To really ramp up the adventure, there are summertime off-trail caving tours, where guides will show you routes that involve lots of crawling and squeezing.
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Lewis & Clark Caverns State Park, MT
Lewis and Clark passed close to the future site of their namesake park in 1805 but didn’t make time in their journey to explore these caves, which is a shame, because they’re well worth a detour. (The park is about 50 miles from Bozeman.) Limestone caves such as this are created by water, and the formations inside are the scenic product of trickling liquid, so it’s perhaps no surprise that they look like icicles and fountains. Though all tours are guided, you can pick your own adventure level: one where the half-mile stroll to the cave mouth is the hardest part (and which cuts straight to the biggest and most striking part of the cave), a slightly more aerobic two-mile meander up and down stone staircases, or a hands-and-knees wild cave tour. Please note that while the park itself is open year-round, the caverns are only accessible May to September.
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Lehman Caves, NV
You’ve heard of stalactites (they hang tight to the ceiling) and stalagmites (which might grow up from the floor to reach them), but at Nevada’s Lehman Caves (part of Great Basin National Park) you can expand your spelunking vocabulary. Look up and discover helictites, which look like suspended coral, and anthodites, which are not unlike stone sea urchins. Most impressive of all is the cavern’s signature Parachute Shield formation—it looks like a subterranean jellyfish (pictured). Pro tip: On your visit, be sure to book the Grand Palace tour—this is the only one that includes the collection of shields.
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Mollie Kathleen Gold Mine, CO
An excellent underground option for the borderline claustrophobic is a tour of the Mollie Kathleen Gold Mine, on the flanks of Pikes Peak just outside Colorado Springs. “The Mollie,” as locals have long called it, functioned as a mine until the 1960s, and now you can tour it to get a sense of what life was like for Western gold miners. The tunnels are wide and well lit, and you ride in a trolley for part of it—no knee pads required here. What the walls of this man-made cavern lack in natural features like stalactites, they make up for in glittering intrigue, as seams of actual gold ore are visible along the tour route.
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Kazumura Lava Tube, Big Island, HI
Everyone knows that volcanoes make changes to the surface of the earth, but less obvious are the dramatic things going on underneath the mountain. See some of them for yourself on a tour of the Kazumura Lava Tube, the longest such tube in the world. You won’t explore all 42 miles of it during your visit, but you will see several scenic caverns that once conducted molten rock, and which today have the hardened remains of magma falls, magma-cicles, dribble spires, and other geologic features similar to those found in more common limestone caves. Discover these formations on one of three tours, ranging in difficulty from one where you just have to be able to handle some short ladders to one requiring rappelling skills.
Note that the Kazumura Lava Tube is located just outside of Hawaii Volcanoes National Park, and was in fact formed by an ancient eruption of Mount Kilauea, the same volcano that closed the park for a time in 2018. While the tube was unaffected by the 2018 eruption, it’ a good idea to check the National Park website to make sure the mountain isn’t hiccupping again when you visit.
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Athabasca Glacier, AB
Most cave tours provide a hint of danger but are actually quite safe if you follow the guide’s instructions. However, the equation changes when the caves are frozen. Ephemeral, shifting, cracking, and occasionally collapsing, ice caves aren’t for everyone. But if you do have experience with ice-climbing gear, the rewards are huge. At the Athabasca Glacier, in Jasper National Park, you can explore the ever-changing system of eerily cobalt-tinged caves waiting to be discovered each winter. Please go with an experienced local guide, though. Not only will you be safer, but he or she might know some secret places where you can really experience unspoiled nature at its best.