Fortaleza San Felipe is a historic Spanish fortress built in the 16th century (1564-1577) to protect Puerto Plata's harbor from pirates and foreign invaders. It later served as a prison during the Trujillo dictatorship. Today it houses a small museum displaying colonial military artifacts, ancient cannons, and weapons. The fortress offers magnificent panoramic views of the Atlantic Ocean and the city's port. Walking around the thick stone walls and moat gives a vivid sense of colonial history.