The Devil's Millhopper

Officially known as the Devil's Millhopper Geological State Park, this massive natural pit has developed its own little environment thanks to the drastically different climate in its depths. 

Stretching down 120 feet into the earth, the sinkhole—known as the Devil's Millhopper—is like a little rainforest right in the middle of Florida. With a muddy pool at the bottom, which is fed by 12 streams on the surface, and a canopy of shade-giving trees around the rim, the temperatures within the hole remain markedly cooler than the sweltering summer heats above. This has allowed the lush greenery in the pit to thrive, creating a damp green environment that is in stark contrast to the surroundings on the surface.

The hole gets its name not only for its shape, which resembles a grain hopper but also from a large number of animal bones and fossils that were discovered on the muddy floor of the site, leading people to imply that the beasts were going down to meet the devil at the bottom. 

A set of winding wooden stairs has been built into the sides of the sinkhole, which leads to a viewing platform at the very bottom where visitors can look upon the bone-filled pond.

Update September 2017: Hurricane Irma damaged the stairs, which may be closed for repairs.

Update: As of June 2019, the stairs are repaired and working again.