Tongue River Cave in Wyoming’s Bighorn National Forest is a dolomite cave shaped by two river channels, including an active underground stretch of the Little Tongue River that joins a dry passage in the Boulder Room. Mapped in 1969, it contains 1.23 miles of passages and reaches 106 feet deep. The cave is known for features such as the Rain Room, strong air currents in a narrow crawl, and waterfalls including Big Falls. Once noted for unusual formations and animal life, it was heavily damaged by unrestricted visitation, vandalism, and theft, and is now managed by the U.S. Forest Service as a sacrifice cave with controlled entry.