La Fortaleza and San Juan National Historic Site

For almost four centuries, the walled city of Old San Juan guarded the entrance to Spain's empire in the Caribbean. La Fortaleza, built from 1533 to 1540 as a fortress at the harbor's edge, has housed the governors of Puerto Rico since 1544, making it the oldest executive mansion in continuous use in the Western Hemisphere. The massive stone forts of El Morro and San Cristóbal, with miles of city walls between them, protected the port from English and Dutch fleets.

Together, La Fortaleza and San Juan National Historic Site, which the National Park Service manages, were named a UNESCO World Heritage Site in 1983. El Morro, its six levels of ramparts rising from the rocks at the mouth of San Juan Bay, is one of the most visited sites in the Caribbean, and the lawn in front of it fills with kite flyers on breezy afternoons. La Fortaleza remains the governor's working office and home, and its blue-and-white facade is a symbol of Puerto Rico.

• Puerto Rico
  The most populous U.S. territory, a Caribbean commonwealth located in