Dry Tortugas: 70 Miles West of Key West

Seaplane or ferry only. The ferry is 2.5 hours through open Gulf (glorious or miserable depending on waves). Seven islands, a coral reef, and Fort Jefferson — the largest masonry structure in the Americas. A hexagonal brick fortress, never finished, never attacked, sitting in the Gulf looking like a movie set nobody made.

16 million bricks shipped from Pensacola by schooner, 1846-1875. Walls eight feet thick, 45 feet high. Dr. Samuel Mudd, who set Booth's broken leg, served his sentence here. The snorkeling off the moat wall is the best in the Florida Keys — wall drops twelve feet in clear water over coral where parrotfish and nurse sharks cruise with national-park confidence.

Ferry $190 round-trip includes snorkel gear and meals. Seaplane $350+ but aerial reef views justify the price. Book weeks out. No shade except inside the fort. The only freshwater is what you carry. The isolation is the point.