The Dry Tortugas are a cluster of seven small islands 70 miles west of Key West, accessible only by seaplane or ferry. The main attraction is Fort Jefferson, one of the largest coastal brick fortifications ever built — a massive hexagonal structure rising from the sea, begun in 1847 and never completed. The fort takes up nearly the entire island of Garden Key.
The ferry from Key West (Yankee Freedom III) takes about two hours each way and spends four hours at the islands. Snorkeling around the fort's moat walls and the surrounding reef is excellent — clear water, healthy coral, and abundant fish. Camping is allowed on the island with a permit; an overnight stay lets you experience the fort at dawn before the day-trippers arrive.