Fort Pickens occupies the western tip of Santa Rosa Island, accessible by road through the Gulf Islands National Seashore. Construction began in 1829, making it one of Florida's oldest surviving military fortifications. The massive brick pentagonal fort remained in Union hands throughout the Civil War — one of only four Southern forts not captured by the Confederacy — and continued in active use through World War II.
The National Park Service manages the site and offers guided tours. The fort's rooms, gun batteries, and tunnels are explorable; the fortification engineering is impressive and the cannon placements still give clear fields of fire over the mouth of Pensacola Bay. The surrounding National Seashore beaches are among the most pristine on the Gulf Coast. Combined with a ferry across the bay to Fort Barrancas, it makes a good half-day military history excursion.