This limestone cave in central Texas was carved by a river that has long since dried up. Now known as Longhorn Cavern (because the wide mouth in its ceiling caused several unsuspecting longhorns to fall to their deaths), the subterranean site has been used by humans for thousands of years. There is evidence that parts of the cave were used to mine materials for arrowheads and other weapons and tools. During the Civil War, Texans mined the caverns for guano (bat poop), which could be used as an ingredient in gunpowder…
