The Fortaleza San Luis is a low stone Spanish colonial fort that overlooks the Yaque del Norte river west of the centre. Built in the 18th century to defend the city against French and English incursions, it later served as a Dominican army base and a prison. Since 2002 it has been a public history museum.
The exhibitions cover Dominican military history, the various wars of independence, and the period under Trujillo. The fort itself is small enough to walk around in an hour, and the views down to the river make it a worthwhile stop. Closed Mondays.