Exploring the subterranean underworld has always had an allure for intrepid adventurers. Hiking above ground is one thing, but scrambling, climbing, and crawling through mysterious caverns provide an adrenaline rush unlike any you’ll get where the sun shines.

Whether you’re a caver or spelunker, the US has a huge amount of cave systems for exploring. Grab an extra layer of clothing and flashlights to explore these cold, damp, and dark expanses — the seven coolest caves you can hike through in America.

Photo: Zack Frank/Shutterstock

1. Mammoth Cave National Park, Kentucky

The Mammoth Cave-Flint Ridge cave system is the largest known cave system in the world, twice as big as the next largest. Over 400 miles have been explored so far, but new caves are constantly being discovered. Entering Mammoth Cave is like being transported to an underground fantasy world reminiscent of the movie “Journey to the Center of the Earth.”

Some of the most famous parts of the cave, like the Frozen Niagara, are lighted. There’s a short Niagara tour or longer ones, such as the four-mile Grand Adventure Tour and the challenging five-mile Wild Cave Tour. If you want to hit the trail independently, more than seven miles of paths weave their way around the visitor’s center. On these paths, you’ll see impressive overlooks into even deeper sections, bubbling springs, and fascinating rock formations.

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2. Carlsbad Caverns, New Mexico

The Carlsbad Caverns are known for their spectacular stalactites and stalagmites, as well as the 400,000-strong colony of Mexican free-tailed bats. Rather than take an elevator, hikers can choose to trek down to the depths of the caves through a dimly lit path of steep switchbacks. At the end of the trail, a limestone cavern known as “The Big Room,” the largest underground chamber in the world, awaits.

The weird and wonderful rock formations are nothing short of astonishing. Make sure to be outside at dusk, so you can see the bats leaving the caves to hunt for insects for dinner. It’s as extraordinary a sight as the caverns below.

Photo: Zack Frank/Shutterstock

3. Wind Cave National Park, South Dakota

Wind Cave National Park earned its name because the sound of the wind, which rushes in and out of the natural cave mouth. A sacred place for Native Americans, the park has 146 miles of explored passages, making it one of the longest and most complex in the world. It’s thought to have the largest number of passages per square mile of any cave.

One of the main features is the unusual mineral formation of boxwork, a calcite resembling honeycomb. It also has frostwork, which looks kind of liked stacked snowflakes, made from mineral deposits. You can take a variety of tours depending on your ability level.

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4. Ape Cave, Washington

A hike through the longest continuous lava tube in the US is not for the faint of heart. There are two caves at Ape Cave, the upper cave being the most challenging, as well as the most interesting. Spelunkers should ensure they are well prepared, wearing gloves to protect themselves from the jagged rocks.

The geology within the upper cave changes throughout. Scrambling over rock piles and scaling an eight-foot lavafall (there is a rope — you don’t have to bring your own) are part of the Ape Cave experience. A skylight tells you that the end of the 1.5-mile hike is imminent. The cave is named after sightings of Bigfoot or Sasquatch in the nearby Mount St. Helens area.

Photo: Michael Landrum/Shutterstock

5. Lava River Cave, Arizona

Formed after a volcanic eruption, when the outer flow cooled and the rushing lava continued to advance, the mile-long hike through Lava River Cave is a perfect spelunking adventure for novices.

The cave is 30-feet high in some places and three feet in others, making it tricky in parts but adding to the adventure. “Lavacicles” hang from the ceiling, and occasional shafts of light shine through small holes. You can see the geological effect of the lava traveling through the tunnel in the smooth arch of the rock.

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6. Balconies Cave, Pinnacles National Park, California

Balconies Cave is a talus cave, meaning that it originated when boulders fell into a canyon rather than being produced by a lava flow. Over time, earthquakes and erosion created a cave roof. Several trails in the park, which range from 2.5-miles to nine-miles long, take you through the Balconies Cave and out the other side. While not as grand as some of the other caves on this list, the Balconies Cave is fun, precisely because entering (or leaving, depending on which side you’re coming from) requires you to scramble over serious boulders in the dark. You really can’t enter this one without a flashlight or headlamp.

If you prefer a cave that’s easier to get into, the Bear Gulch Cave — also a talus cave — has stairs and railings set in the rocks, making it easier to get through. It’s still a tight squeeze to get inside and, like Balconies, it may be wet on the ground in winter. It will be a cool, welcome break from the heat in late summer, though. Both caves close between mid-May and mid-July to accommodate the nesting season of the resident Townsend’s big-eared bats.

Photo: Jason L. Price/Shutterstock

7. Blanchard Springs Caverns, Arkansas

Blanchard Springs Caverns has eight miles of surveyed passages. While you can hike most of the caves on this list on your own, you need to view Blanchard Springs with a guided tour. On the Wild Cave tour, you’ll crawl through narrow spaces and slither along mudslides in underdeveloped parts of the cave.

Although the Dripstone Tour is easy, it’s spectacular. Passing through two huge caverns with an array of sparkling crystalline formations, columns, flowstones, and a natural bridge, the rocks are accentuated with illuminations. The Discovery Tour is more strenuous, descending into the depths to follow the cave stream to the natural entrance, which was discovered by the original explorers.

Although many caves in the southeast have been closed to protect resident bat populations from the white-nose syndrome, Blanchard Springs remains open.