The earth over a subterranean river has collapsed creating a beautiful swimming hole in a cavern with a 'window' near Williston, Florida. 

 

The water holds at a comfortable 72 °F degrees making it a popular year-round recreation destination. The ominous name, Devil's Den came from the visible plume of steam that rises though the cavern top on cold mornings which looked like a chimney stemming from Hell to early Floridians.

 

The 'den' and river system are privately owned and  currently operating as a SCUBA diving training and recreational facility. There are several underwater tunnels that shoot off from the main cavern opening. One of the most alluring is chamber 3 where ancient artifacts with animal and human remains rest about 70 feet under water. The remains date back to 7,500 BC and include that of a saber-toothed tiger and mastodons.

 

The Devil's Den is also known for it's deadly nature. The sign to the left has been posted with a fence in one of the deepest and deadliest passages. The river system is naturally high risk due to very low water flow, high-silt and cramped pathways. Though special dive certificates are required to enter underwater caves, not all adhere to the rules and warnings and dive without proper training or equipment resulting in casualties.