Pick up a map at the entrance and head out on a self-guided tour of this massive fortress that has guarded the San Juan Bay for 500 years. Park rangers give an English presentation at the top of every hour, and an English movie runs on the hour and half-hour. Both are short, free, and interesting.
The three flags flying over this UNESCO World Heritage Site are the United States flag, the flag of Puerto Rico, and the Cross of Burgundy flag, which was once used by the Spanish military.
The six-level Citadel surrounds the Main Plaza, where troops once assembled for inspection and drills. On the upper level, you’ll find photogenic garitas or sentry boxes set into the outer wall. Notice the lighthouse that was hit by U.S. fire during the Spanish-American War and rebuilt by the U.S. in 1908. Wander down the tunnel of the old tower, Torre Antigua, and inspect the walls for shell fragments left by U.S. forces in 1898. This area of the fort is the oldest, built in 1539. Other interesting areas include the cannon water battery, which has fantastic views of the harbor, and the kitchen, where meals were prepared for troops.