La Fortaleza (palace) built
1533 CE.
Shown on the map at 18.464°, -66.119°.
La Fortaleza (English: "the fortress"), also known as the Palacio de Santa Catalina ("Saint Catherine's Palace"), is the official residence and workplace of the Governor of Puerto Rico. Located in the historic quarter of Old San Juan in the capital city and municipality of San Juan, it has housed the governor since the 16th century, making it the oldest executive seat in continuous use in the New World. Built as a medieval fortress from 1533 to 1540 by orders of King Charles I of Spain and remodeled to its present Neoclassical style in 1846 by orders of Governor Rafael Arístegui, it was the first fortification erected by the Spanish on San Juan Islet to defend San Juan Bay, the harbor of Old San Juan. Alongside El Morro, San Cristóbal, and other forts part of the Walls of Old San Juan, it protected strategically and militarily important Puerto Rico, or La Llave de las Indias (The Key to the Indies), from invasions by competing world powers and raids from privateers and pirates during the Age of Discovery and Sail.
Text from the Wikipedia article La Fortaleza, licensed CC BY-SA 4.0.