No, there are no live sharks in Devil's Den Prehistoric Spring, which is a privately owned geological sinkhole and scuba diving center in Williston, Florida. The spring is a landlocked, freshwater cavern with a constant temperature of 22°C (72°F). However, Devil's Den is world-famous for its fossilized remains, including those of prehistoric animals. While you won't find a shark swimming next to you, paleontologists have discovered fossils of extinct Pleistocene-era creatures in the underwater chambers, such as mastodons, ground sloths, and even saber-toothed cats. Because the spring is fed by an underground aquifer and has no connection to the ocean, it is an entirely enclosed system. The only "monsters" you might encounter are the large grass carp or turtles that occasionally swim in the crystal-clear waters. It remains a popular spot for divers and snorkelers specifically because it offers a safe, predator-free environment with stunning prehistoric scenery and a unique "chimney" opening that creates dramatic sunbeams in the cavern.