Natural Bridge Caverns in the Texas Hill Country near San Antonio is the state’s largest commercial cavern, named for a sixty-foot limestone bridge left suspended above its entrance after a sinkhole collapse. The cave is known for large, still-forming calcite speleothems created as rainwater seeps through limestone and drips below ground. Discovered in 1960 by four Saint Mary’s University students, it was developed with Clara Wuest’s private financing and opened to the public in 1964. A U.S. National Natural Landmark since 1971, the site has also yielded ancient artifacts and extinct animal remains, while exploration continues to uncover new passages.