At the northwestern tip of the Old City is El Morro ("the promontory"), a fortress built by the Spaniards between 1539 and 1786. Rising 140 feet above the sea, the massive six-level fortress was built to protect the harbor entrance. It is a labyrinth of cannon batteries, ramps, barracks, turrets, towers, and tunnels. Built to protect the port, El Morro has a commanding view of the harbor. You're free to wander throughout. The cannon emplacement walls and the dank secret
passageways are a wonder of engineering. The fort's small but enlightening museum displays ancient Spanish guns and other armaments, military uniforms, and blueprints for Spanish forts in the Americas, although Castillo San Cristóbal has more extensive and impressive exhibits. There's also a gift shop. The fort is a National Historic Site administered by the U.S. Park Service; it's a World Heritage Site as well. Various tours and a video are available in English.