I loved visiting the historical sites in Old San Juan. Make sure to visit:
La Fortaleza and San Juan Historic Site: I enjoyed seeing these UNESCO World Heritage Sites in Old San Juan. One of the major sites is the Castillo San Felipe del Morro, or El Morro Fort, which are massive fortifications built on a rocky peak of land to protect San Juan Bay. It is a triangular bastion that is well worth the visit. The cemetery below, Santa Maria Magdalena de Pazzis, is amazing with its tombs and beautiful structures. La Fortaleza is a beautiful structure that is the residence of the Governor of Puerto Rico. The gardens are open for daily visits.
Ballaja Barracks: Walk through the former barracks near the El Morro Fort which has been restored to its original beauty.
San Juan Gate: Walk under La Fortaleza to the Paseo de la Princesa along the water. Here you will see the San Juan Gate, the former entrance to the city. Nearby is the interesting sculpture la Rogativa showing a priest leading a religious procession, in 1797, when the British attacked Old San Juan.
Castillo San Cristobal: I also walked through Castillo San Cristobal which is another historical fort. It is the biggest European fortification in the Americas. On Tuesdays at 6 pm (and I read Sundays also) they have a music and dance performance by the Ballet Folklorico as part of the National Park’s cultural mission. It was a nice backdrop by which to tour the large structure.
Plaza Colon: An attractive plaza next to Antiguo Casino and Teatro Tapia with a large statue of Christopher Columbus.
Catedral de San Juan Bautista: One of the oldest churches in the Americas, this church is worth the visit though it is not elaborately decorated. It is located at Calle del Cristo #151-153.