Eichelberger Sink (Lake Alfred)
Sinkholes are a common formation in Central Florida. They are formed when supporting underground water recedes from a cavity in the aquifer, causing the ground to collapse into the cavity. Most lakes in the area were formed in this fashion. 
The 100-yard -wide, 60-foot-deep Eichelberger Sink, shown here in a 360-degree cyclorama taken from its center,  is unusual in that it is dry part of the year, filling with water and becoming Lake Alfred during the summer rainy season. It is to my knowledge the only periodically dry lake in Florida.