Located in Old San Juan, the forts of El Morro and San Cristobal serve as the guardians of the Caribbean. Both forts, located within a mile of each other, were constructed in the 16th century by Spain in order to guard both Puerto Rico and its ports. The forts were later taken over by the US and used during WWII and on into the 70's. They have been well taken care of and are definitely not to be missed during a trip to Puerto Rico! If you aren't super into history, it is a great place to catch the ocean breeze and amazing views.