The Eco Discovery Center is one of the places I love to visit. http://eco-discovery.com/index.html It is free, but accepts donations. We visit every time we come to the keys.
We thoroughly enjoy looking at all of the different corals and crustations. I just love the movie shown at the Eco Center too. Near by is Fort Zachary Taylor http://www.floridastateparks.org/forttaylor/. We have been to two other forts on the Island, but this was our first visit to Fort Zachary Taylor.
Construction was started in 1845 and not completed for 21 years. Captain John Brannan claimed the fort for the Union in 1861. It never saw hostile action because it was very well fortified. We learned about the three main types of cannons that were part of the artillary. Marc showed Marcus and Caroline how the cannons would have been used.