Williston, Florida, United States

Devil's Den

Devil's Den is a karst window — a small surface opening into a larger underground freshwater spring system — about 90 minutes north of Orlando near Williston, Florida. The name comes from the column of warm steam that rises through the entrance hole on cold winter mornings, when the 22 C spring water meets cold air. The pool is privately owned and operated as a year-round dive facility. The dome of limestone above the water has a single skylight opening that lets a beam of sunlight stream onto the rock-and-sand bottom 16 metres below. The water is gin-clear with visibility regularly above 30 metres. There is no live coral or fish to speak of, but the cave walls are decorated with karst features and prehistoric mammal fossils have been recovered from the floor: extinct horses, ground sloths, mastodons, dating back roughly 33,000 years. Cavern training with line is required to penetrate the side passages; the open pool is open to all open-water divers.