Airmen's Cave, beside Barton Creek in south Austin within the Barton Creek Greenbelt, is a long, narrow Edwards limestone cave known for sustained crawls and tight passages rather than large rooms. Formed in the early Cretaceous, it once carried water toward Barton Springs before changes in the water table left its intricate low-profile network dry. Discovered in 1971 by two airmen from Bergstrom Air Force Base, it was explored and surveyed over the next three years by the University of Texas Grotto. The cave is also important for rare troglobite species, while heavy visitation, a 2007 rescue, and growing safety and habitat concerns led to a security gate in 2012.