The SuwanneeRiver valley is riddled with artesian springs.  The openings created by the springs develop into stunning open pools.  The water is perfectly clear.  It is unbelievably blue.  The surface constantly simmers as the water boils up from underground.  Warm, swirling, spring water creates complex erosion patterns in the walls and floors of the pools.  Awesome.

They scuba dive in these things.  Especially the ones they call jug formation springs where the discharge is actually a necked down section that rises from a larger underground cave or series of caves.  They dive down through the neck, against the flow of the spring (think million of gallons a day) into the chambers below.  How nuts is that?