Crystal Cave, Marble karst cave in Sequoia National Park, United States.

Crystal Cave is a marble karst cave in the Giant Forest area of Sequoia National Park, in the western Sierra Nevada of California. It is the only one of the park's at least 240 known caves open to the public. The cave mouth is a broad, low opening in a layered tan, grey and brown rock face, with moss and small plants on the overhang and a pale dirt floor running inward past a few dark rounded rocks.

Crystal Cave is a marble karst cave, not a limestone one, in Sequoia National Park. The cave lies in the Giant Forest area between the Ash Mountain entrance and the Giant Forest Museum, and is reached by the Crystal Cave Trail. It is one of at least 240 known caves in the park but the only one open to the public.

Crystal Cave is reached on foot by the Crystal Cave Trail, and entry is only with a guide from the park service. Guides explain the marble karst and the cave biology and karst management studied and managed by Sequoia and Kings Canyon National Park.

Tickets are not sold at the cave; buy them in advance through SequoiaParksConservancy.org, and entry is by guided tour only. The cave stays at a constant 48 °F (9 °C), so bring a layer. The walk in follows the Crystal Cave Trail from the Giant Forest area, between the Ash Mountain entrance and the Giant Forest Museum.

Crystal Cave is the only one of at least 240 known caves in Sequoia National Park that the public can enter. The rest stay closed, so a guided tour here is the park's single chance to go underground. Look for the broad, low mouth in the rock face, roofed with layered tan, grey and brown stone and mossy at the overhang.