"Set 110 kilometers (70 miles) south of Key West is a group of seven uninhabited islands known as the Dry Tortugas, which makes for one of the area’s top day trips. It is one of 11 national parks in Florida . Once there you can explore the historic Fort Jefferson, an enormous military facility that was under construction for 30 years (1846–1875) but never completed. The isles are surrounded by coral reefs with great snorkeling in the crystal clear blue waters, and you can also see birdlife galore. Most visitors arrive by ferry, which takes about three hours each way and includes a four-hour stay on the islands, but you can also charter a seaplane for a hefty price."