Key Largo may seem underwhelming at first glance, but “under” is the key word, as the main sights are underwater, past the touristy shops and motels. The 33 mi (53 km) island is the longest in the Florida Keys; it also has the Keys' biggest concentration of dive sites.
John Pennekamp Coral Reef State Park is a must stop. The first underwater park in the U.S., Pennekamp provides some pleasant beaches, decent nature trails, and colorful coral reefs. An aquarium at the visitor center provides a glimpse of what’s under the water, and a glass-bottom boat tour shows the real thing.
If you want to go deeper, take a snorkeling trip or a diving excursion. After a day of activity, stop for seafood in one of the many restaurants on the key.