The Devil's Millhopper is a large sinkhole, 117 feet deep and about 500 feet across. The name comes from the shape of the hole, resembling the funnels used in mills to feed the grain into the millstone, and the fact that numermous bones and skeletons of animals have been found along the sides and bottom, leading many people to think that the Devil opened up a hole to suck all down to Hell.
Other than that, that's it.
The Devil's Millhopper is located in northern Gainsville and as haunts go, there are none. But as a nature walk, it's impressive. There's a boardwalk leading down about 100 feet to the bottom and halfway across. It's a large deep bowl like formation.
Sinkholes are caused by rainwater seeping through the ground, where it filters through old rotten vegetation where it turns into a very weak acid. The bedrock of Florida is primarily limestone, a rather porus rock that reacts with acid readily. The limestone is eaten away, leaving a large cavity underground that will eventually collapse under the weight of the ground above.
And that's what happened with the Devil's Millhopper. The primary sink hole was made approximately 15,000 years ago, but recent openings have happened in the last millenium, one possibly a hundred years ago.