Saltpeter Cave, a limestone cave in Carter Caves State Resort Park near Olive Hill, Kentucky, stretches about 3.05 kilometers and has long been known for both history and ecology. Also called Swingle's Cave and Swindell's Cave, it was being mined for saltpeter by the early 1800s. Local tradition connects its niter to gunpowder made during the War of 1812, including supplies tied to the 1815 Battle of New Orleans, linking the cave to early American industry and warfare. Its entrance features a distinctive mid-20th-century limestone and iron gate, and today the cave is especially important as a winter hibernation site for the endangered Indiana bat.