10 Caves in the U.S. That Feel Like Another Planet

Beneath the United States lies a surprising network of caves shaped over millions of years. Some feel almost otherworldly, with strange rock formations and the occasional glow from naturally occurring minerals. Each cave tells a part of a larger story written in stone, layer by layer.

Mammoth Cave National Park

Mammoth Cave National Park in Kentucky holds centuries of geological history in its 426 miles of mapped passages. The size alone is impressive, but the details are vast chambers, narrow corridors, and formations shaped by water and time. Those craving more depth can follow the Historic Tour through shadowy stretches like Bottomless Pit.

Carlsbad Caverns National Park

Carlsbad Caverns National Park in New Mexico features one of North America's most expansive underground chambers. A steady 56°F (13°C) inside offers relief from the desert climate above. Thousands of Brazilian free-tailed bats exit the cave at dusk in a coordinated flight between late May and October. The Bat Flight Program offers seating and ranger-led talks during this event.

Wind Cave National Park

Wind Cave National Park in South Dakota is home to more than 154 miles of underground passages, making it one of the longest cave systems in the world. It's best known for box work—thin, honeycomb-like calcite formations rarely found anywhere else. On the surface, visitors can hike through prairie land filled with bison, elk, and prairie dogs.

Kartchner Caverns State Park

Discovered in 1974 and kept secret for over a decade, the limestone passages beneath southern Arizona hold some of the region's best-preserved cave formations. Kartchner Caverns State Park features a 58-foot column known as Kubla Khan and a 21-foot soda straw stalactite—both standout examples of slow geological change.

Lehman Caves

Located in Nevada’s Great Basin National Park, Lehman Caves extends for more than two miles through marble rock and is known for its rare shield formations—thin, flat structures that project from cave walls and ceilings. The cave was first documented in the late 19th century and has since been a site of geological and historical interest.

Meramec Caverns

Formed over 400 million years ago, Meramec Caverns in Stanton, Missouri, spans 4.6 miles of limestone passages. It features several uncommon formations, including the Wine Table—a natural onyx structure formed underwater—and the Stage Curtain, one of the largest known cave formations. The Mirror Room stands out for its visual effect, where a shallow stream reflects the ceiling, creating the appearance of a deep vertical drop.

Ruby Falls

Ruby Falls, located within Lookout Mountain in Chattanooga, Tennessee, features a 145-foot underground waterfall—the tallest and deepest accessible to the public in the United States. Discovered in 1928, the site requires a 260-foot elevator descent followed by a guided, one-mile round-trip walk. The route ends at the illuminated waterfall, framed by natural formations shaped over millions of years.

Timpanogos Cave National Monument

A 1.5-mile trail leads to the entrance of Timpanogos Cave National Monument in Utah, offering wide views of American Fork Canyon. The trail passes through limestone embedded with fossilized shells and coral, remnants of an ancient seabed. Explorers also encounter a variety of unique formations like helictites—delicate, gravity-defying mineral structures—and the "Heart of Timpanogos," a stalactite resembling a human heart.

Oregon Caves National Monument and Preserve

High in Oregon’s Siskiyou Mountains, Oregon Caves National Monument and Preserve reveals a marble cave system shaped over millions of years. Discovered in 1874, the cave stretches through narrow corridors and large chambers that can be explored on guided tours. Outside, the forested preserve supports a range of plants and animals native to the region.

Sea Lion Caves

About 11 miles north of Florence, Oregon, Sea Lion Caves holds the title of the largest sea cave in the United States. Formed roughly 25 million years ago, the main cavern covers about two acres with a ceiling that rises 125 feet. Steller sea lions gather here seasonally, using the space as a natural haul-out and breeding site.

Lava Beds National Monument

Lava Beds National Monument in northeastern California holds over 800 lava tube caves beneath its desert, all created by eruptions from Medicine Lake Volcano. These tunnels vary in size and complexity, with the Cave Loop offering options for different experience levels. The monument also offers educational programs for younger visitors, connecting the volcanic geology with the region’s wildlife and cultural history.

Lost Sea Cave

Beneath Sweetwater, Tennessee, Craighead Caverns holds a lake stretching over 4.5 acres—America’s largest underground lake and the second largest in the world. First discovered in 1905 by a teenager exploring with a lantern and mudballs, the site now features guided tours. The cave also contains anthodites—rare crystal formations that resemble tiny, spiky blossoms found in only a few locations worldwide.

Niagara Cave

In Harmony, Minnesota, Niagara Cave drops nearly 200 feet and features a 60-foot underground waterfall, exposed fossils over 450 million years old, and mile-long passageways. First discovered in 1924 after livestock disappeared into a sinkhole, the cave has since revealed striking formations like stalactites and stalagmites, along with a small wedding chapel where hundreds of couples have exchanged vows.

Jewel Cave National Monument

Jewel Cave National Monument in South Dakota contains over 220 miles of mapped passages, making it the second-longest cave in the United States and fifth-longest in the world. The calcite crystals—nailhead and dogtooth spar—that cover many of its walls are responsible for the cave's name. Notable formations include frostwork, gypsum “flowers,” and hydromagnesite balloons shaped by mineral-rich water.

Marengo Cave

Marengo Cave in southern Indiana was discovered in 1883 by two local children. The 40-minute Crystal Palace tour includes formations like Mirror Lake, where still water creates a clear reflection of the cave ceiling. The Dripstone Trail, lasting about an hour, includes soda straws, tall stalagmites, and the Penny Ceiling—where coins often stick to a layer of damp cave mud.