The Devil’s Sinkhole, located a few miles northeast of Rocksprings along State Highway 377, is a National Natural Landmark and believed to be the largest known single-room cave in the state. It’s also home to millions of Mexican free-tailed bats from spring to fall. The Sinkhole cavern, three hundred and fifty feet deep, has an abrupt opening as if someone had punched a hole in the surface. It drops in a long, chimney-like neck then ends in a broad bowl carved by water. The bowl, shaped like the bottom half of an hour glass, holds a mountainous cone of breakdown, the result of the neck collapsing layer upon layer all the way to the surface as the rock fell away and into the enormous cavern below. The bats reside along the high ramparts of the bowl and the breakdown cone is layered several feet thick in their guano. The bats leave the Sinkhole in a nightly exodus, rising in a smoke-like tornado called a bat column, before riding the prevailing currents and feeding on insects thousands of feet in the air. Devil’s Sinkhole State Natural Area bat flight observations can be arranged through the nonprofit Devil’s Sinkhole Society, a “friends of the Devil’s” organization formed in 2001 as a partnership with Texas Parks and Wildlife. The group’s Visitor Center is located on the corner of Rocksprings’ town square, just a block from the Historic Rocksprings Hotel.