A star of Old San Juan, brooding El Morro sits atop a headland, deterring would-be attackers. The 140ft walls (some up to 15ft thick) date to 1539 and it's said to be the oldest Spanish fort in the New World. Displays, a short video and weekend tours document the construction of the fort, which took almost 200 years, as well as its role in rebuffing attacks on the island by the British, the Dutch and, later, the US military.

　　At a minimum, try to make the climb up the ramparts to the sentries’ walks along the Santa Barbara Bastion and Austria Half-Bastion for the views of the sea, the bay, Old San Juan, modern San Juan, El Yunque and the island’s mountainous spine. Wear comfortable shoes for the long walks and countless staircases.

　　On weekends, the fields leading up to the fort are alive with picnickers, lovers and kite flyers. The scene becomes a kind of impromptu festival with food carts on the perimeter.

　　The gray, castellated lighthouse on the 6th floor has been in operation since 1846 (although the tower itself dates from 1906), making it the island’s oldest light station still in use today. After suffering severe damage during a US navy bombardment during the 1898 Spanish–American War, the original lighthouse was rebuilt with unique Spanish-Moorish features, a style that blends in surprisingly well with the rest of the fort.

　　The National Park Service maintains this fort and the small military museum on the premises. It was declared a Unesco World Heritage site in 1983.