The Caves Trail at Craters of the Moon National Monument leads into one of the most otherworldly landscapes in Idaho: a field of lava tubes formed by ancient volcanic eruptions on the high sagebrush desert of the Snake River Plain. Along this short trail, four remarkable caverns lie open to explorers, offering a rare chance to descend beneath the black lava into cool, dark tubes left behind by rivers of molten rock thousands of years ago. It's the highlight of a monument that genuinely looks like another planet.

Four caves are accessible from the trail, each with its own character. Indian Tunnel is the star, the largest and longest, measuring about 30 feet tall and 800 feet long, with several massive collapsed skylights that let in so much daylight you don't even need a flashlight to walk through it. Boy Scout Cave is the opposite experience: it holds onto its winter chill all year and keeps ice on its floor even in summer. Dewdrop Cave and Beauty Cave round out the quartet, darker and requiring real light.

A free permit is required to enter any of the caves, and it matters: the permit program exists to protect the monument's bats from white-nose syndrome, a devastating disease spread on gear and clothing. You pick up the free permit at the entrance station, the visitor center, or on a ranger-guided walk, and rangers may ask whether your gear has been in other caves. Bring at least one good light per person for the darker caves, and a warm layer, since the tubes stay cold year-round.

The landscape between the caves is part of the experience: a jagged, black expanse of lava with almost no shade, which bakes in summer, so early or late in the day is far more comfortable, and sturdy shoes are essential on the sharp, uneven basalt. The trail itself is relatively short, but exploring all four caves makes for a genuine half-day adventure.

Craters of the Moon sits in central Idaho along the Snake River Plain, an easy detour off the highway between Arco and Carey. Between walking through the skylit cathedral of Indian Tunnel and standing on ice in Boy Scout Cave in July, the Caves Trail is the unmissable heart of one of the strangest and most fascinating parks in the country.