La Fortaleza (Calle Fortaleza, Old San Juan, 787/721-7000, ext. 2211, 2323, and 2358, Mon.–Fri. 9 a.m.–3:30 p.m., free) was the first fort built in Puerto Rico , completed in 1540 to provide refuge for the island’s original Spanish settlers. Partially burned by the Dutch in 1625, it was rebuilt in the 1640s and received a new facade in 1846.
La Fortaleza has been the official residence of the governor of Puerto Rico since the 16th century, which gives it the distinction of the longest continuous use of an executive mansion in the western hemisphere. Tours are limited mostly to the lovely gardens and first floor, with audio narration in Spanish and English.