I love colonial Spanish architecture. All the arches, the tiles roofs, the vibrant colors. Viejo San Juan or Old San Juan, was a beautiful example of it. I spent an entire day to roam the endless halls, tunnels, and enormous fields of Castillo de San Cristobal. A stunning, expansive fortress on the edge of the sea that combined with San Felipe del Morro Fort and Fortin San Juan de la Cruz to protect English and Dutch invaders from taking Puerto Rico - Spain's "gateway to the the Caribbean."