Walls of Old San Juan in the context of "Castillo San Felipe del Morro"

Castillo San Cristóbal (English: Saint Christopher Castle) is a fortress in the Old San Juan historic quarter of San Juan, the capital municipality of Puerto Rico, known for being the largest fortification built by the Spanish in the New World. Dating back to defense expansions following attacks by the English in 1598 and Dutch in 1625, it was first constructed in 1634 as the Caballero de San Miguel (Saint Michael Cavalier) and the Garita del Diablo ("devil’s sentry box"). Over the next 150 years, especially in the reign of King Charles III of Spain, it continued to be developed into a bastion fort with outer ravelins and batteries to reach its largest size in 1783. Rising 150 ft from the Atlantic shoreline, the three-level edifice stands on a hill at the northern coastline of San Juan Islet, guarding the land entry to Old San Juan. Alongside El Morro, La Fortaleza, 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 invasion by competing world powers during the Age of Sail. It was designated a World Heritage Site by UNESCO in 1983.

La Fortaleza (English: "the fortress"), officially 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 municipality of San Juan, it has served as the governor’s residence since the 16th century, making it the oldest executive mansion 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 y Vélez, 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 invasion by competing world powers and harassment by privateers and pirates during the Age of Discovery and Sail. It was designated a World Heritage Site in 1983.

Situated in the western end of San Juan Islet in the Old San Juan historic quarter, La Fortaleza, seat of the executive branch, is about 1 mile (1.6 km) from the Capitol of Puerto Rico, seat of the legislative branch, in the center of the Islet in the Puerta de Tierra historic district, and 2 miles (3.2 km) from the Supreme Court Building, seat of the judicial branch, in the eastern end of the Islet in Puerta de Tierra.

The Capitol of Puerto Rico (Spanish: Capitolio de Puerto Rico), also known as Casa de las Leyes (House of Laws), and most commonly referred to as El Capitolio (The Capitol), is the seat of the Legislative Assembly of Puerto Rico, a bicameral legislature composed of a Senate and a House of Representatives responsible for the legislative branch of the government in the archipelago and island. Located in San Juan Islet immediately outside the city walls of the Old San Juan historic quarter in the capital municipality of San Juan, the ocean and bayfront, Neoclassical Beaux-Arts style, entirely white marble-cladded edifice was built by architect Rafael Carmoega between 1921 and 1929 to resemble the Pantheon in Rome, using as inspiration the Low Memorial Library in New York City. It was added to the U.S. National Register of Historic Places in 1977.

Situated in the center of San Juan Islet in the Puerta de Tierra historic district overlooking the Atlantic Ocean in the north and San Juan Bay in the south from an elevated point, the Capitol of Puerto Rico is about 1 mile (1.6 km) from both the La Fortaleza, seat of the executive branch, in the Old San Juan historic quarter in the western end of the Islet, and the Supreme Court Building, seat of the judicial branch, in the eastern end of the Islet in Puerta de Tierra. The Court and Capitol are directly connected via Luis Muñoz Rivera Avenue in the north and Juan Ponce de León Avenue in the south, both of which are directly linked to La Fortaleza via San Francisco Street in the north and Fortaleza Street in the south.