Photographer: Kevin Stillman

The Sinkhole is a vertical cavern with an opening approximately 40 x 60 feet and a vertical drop to the main cavern of about 140 feet. The main cavern is circular and reaches a total depth of 350 - 400 feet. Freshwater lakes around its perimeter support an endemic amphipod, and a rare aquatic isopod. Both are crustaceans. There is a large seasonal population of Mexican freetail bats which put on an evening show when they leave the cave to forage. Tours to see the bats are available from mid-Apr. through mid-Oct, and guided tours to the cavern are available every evening.