2 good choices: the Royal Palm visitor centre west of Homestead (south of Miami) is a great place. Go in the morning and there will be no tour busses and the like. You'll see large alligators really up close and personal, as well as turtles and all sorts of birds.

Alternatively, drive west on the highway that skirts MIA on the south side and go to the Shark Valley visitor centre. I'd rent a bike and ride anticlockwise. Again, you'll see large alligators very close and personal.

FWIW, southern Florida is pretty much dead flat except for highway overpasses.