Fort San Felipe was built in 1564 by order of Philip II of Spain and is Puerto Plata's oldest surviving building.
It was a formidable construction, designed to strike fear into any would-be-invader's heart. Its 2m- (7ft) thick walls, squat doorways and moat filled with sharp coral and swords served to keep people out and, when the fort later became a prison, worked just as effectively at keeping people in - including one of its most notable captives - Juan Pablo Duarte, who served time here in 1844.
The tower contains a small museum of wartime artifacts such as guns, artillery shells, and cannonballs. Fort San Felipe's main attraction, however, is its sweeping views across the Atlantic.