The Dolphin Research Center is about halfway between Miami and Key West and makes for a nice break on a rather long drive. I had thought it would it be great fun to swim with a dolphin, but discovering that it cost over a hundred dollars for a few minutes in a small pen wearing a life preserver and having limited contact with the dolphin, I passed.
The basic tour is fairly informative yet brisk. The trainers seem to be protective of the dolphins and don't badger them in to doing too many tricks. More advanced classes are available through the Dolphin Research Center if you are interested in becoming a dolphin trainer, and the volunteer positions sound fun.