Crystal Cave is a marble karst cave in Sequoia National Park in California’s western Sierra Nevada, located in the Giant Forest area between the Ash Mountain entrance and the Giant Forest Museum. Among at least 240 known caves in the park, it is the only one open to the public. The cave remains at a constant 48 degrees Fahrenheit, or 9 degrees Celsius, inside. Visitors can enter only on guided tours arranged through the Sequoia Park Conservancy, and tickets must be purchased in advance rather than at the site.