Devil's Den Cave near Williston, Florida, is a karst window created when the roof above an underground river collapsed, exposing a water-filled cavern far larger below than its small surface opening. Its constant 72 degree water and cold-weather vapor plume gave it a dramatic name. Beyond its unusual geology and appearance, the cave is a major archaeological and paleontological site. In a deep underwater passage, scientists found human remains and artifacts alongside fossils of extinct Pleistocene animals, indicating they were of roughly the same age. Now privately owned, it operates as a recreational and SCUBA training site while remaining an important Ice Age fossil locality.