Founded in 1521, San Juan is the second-oldest European city still existing in the Americas, only a few years behind Santo Domingo. It soon became important as the first port of call for Spanish ships en route to the New World, and was therefore a popular target for the English (including Francis Drake), French, and Dutch, as well as for pirates of all kinds. To secure the port, the Spanish built 2 massive fortifications and a large city wall. These form the San Juan National Historic Site, a unit of the U.S. National Park Service. The fortress of San Cristóbal is the largest fortification built by the Spanish in the New World. About a 20-minute walk away, San Felipe del Morro guards the entrance to San Juan Bay. The most fascinating feature of this fort is the large open space in front, which was intended to give the defenders an open field of fire. You can easily spend several hours exploring each of the forts. They are connected by the remains of the city wall, which also stretches south of El Morro to include San Juan Gate, for centuries the only way to enter the city. The WH site also includes La Fortaleza, built in the 16th century as yet another fortification but soon found to be inadequate for this purpose and turned into the residence of the governor of Puerto Rico (it is also known as Santa Catalina Palace). It still fulfills this function today, and is thus the oldest executive residence still in use in the New World. Today it is not very difficult to visit; you just show up and register for the next guided tour. I actually had a tour guide completely to myself, and for all of the 30 or so minutes that I was shown around La Fortaleza, a security agent discreetly accompanied us. The inside is quite interesting, but the highlights of this WH site are definitely the 2 fortresses. San Juan is in general a pleasant city, and the historic centre, known as Old San Juan, is at all times full of tourists from the many cruiseships lying at anchor.