Castillo San Felipe del Morro (El Morro)

Castillo San Felipe del Morro — 'El Morro' — guards the rocky point at the entrance to San Juan Bay, a six-level Spanish citadel begun in the 16th century to defend the harbor from seaborne attack. Its sloping outer walls, vaulted casemates, ramped batteries, and round sentry boxes (garitas) climb more than 140 feet above the water, topped by a lighthouse.

It anchors the San Juan National Historic Site, a UNESCO World Heritage Site run by the U.S. National Park Service, and opens onto a broad grassy esplanade where families fly kites on breezy afternoons. One ticket covers both El Morro and nearby Castillo San Cristóbal; allow an hour or two to wander the tunnels, dungeons, and ramparts and take in the views across the bay and Old San Juan's rooftops.