El Castillo de San Felipe del Morro
More commonly known as El Morro, this stone garrison is the oldest freestanding fort in the Americas. Built between 1539 and 1797 by Spanish settlers on a rock-strewn promontory at the entrance of the San Juan Bay, it's a hulking pile of turrets, towers, walls, barracks, and dungeons that are wonderful to explore. A combination pass buys entry to both El Morro and Castillo San Cristóbal, another fort on the northeast edge of Old San Juan; it's larger than El Morro and usually less crowded.
Tune in on Wednesdays at 10PM ET for Top Chef: Boston, the 12th season of Bravo's Emmy-Award winning, hit reality series.