San Juan National Historic Site is on the north shore of Old San Juan overlooking the bay. The extensive site contains the fortifications built by the Spanish to protect San Juan and the treasure-laden fleets that sailed past the city en route to Spain. Puerta de San Juan at the foot of Caleta de San Juan is the most impressive and last remaining of six gates of the old city wall. The 1639 structure stands more than 16 feet (5 m) tall.
The site encompasses two large forts and a small inlet fortification, Castillo de San Juan de la Cruz. El Cañuelo, as the smallest fort is known, was built on Isla de Cabras at the entrance to San Juan Harbor, about 1610 as a wooden structure. Destroyed by the Dutch in 1625, it was rebuilt in stone in the 1660s. The tiny fort is closed to the public.
Guided tours of the national historic site are available by reservation. Comfortable walking shoes are recommended.