Fort San Juan de Ulúa (Castillo San Juan de Ulúa), in the harbor on Gallega Island, can be reached from coastal hwy. Mex. 180 by taking the Puente Montecitos exit to the port area (Zona Industrial Portuaria); from the city center, take Blvd. Fidel Velazquez to the port area, following signs. This massive fort was built by the Spanish to protect their New World interests. Construction of the thick coral walls began in the 1530s but was not completed until the late 18th century. It later served as a place of incarceration for political prisoners; even Mexican president Benito Juárez was held here.
The floating fortress, declared a historical monument in 1962, is connected to the mainland by a small walking bridge. Visitors can venture into dank prison cells and view guard posts, the remains of cannons and docking areas where gold was stored. Today this ancient rampart is surrounded by huge cargo container ships. A guided tour is recommended, since there is no signage or brochure.
Taxi fare to the fort from the city center is about 70 pesos. Boats depart for the fort from the malecón, across from the Hotel Emporio, whenever there are enough passengers; the fee is 35 pesos per person.