An imposing Portuguese-Dutch construction, this fortress is situated right by the causeway to the island and is ringed by a moat. It's a bit shambolic, but the walls are atmospheric and contain the roofless remains of a chapel, dungeon and Dutch bell tower. Climb the ramparts for an impressive perspective of the town and the Gulf of Mannar. Don't miss the carved details on the entrance to the central courtyard (where you can park).
The fort was built in a quadrangular layout by the Portuguese in 1560, but captured by the Dutch in 1658, who rebuilt it in 1695, adding four bastions. A century later, the colonial merry-go-round turned again as the British occupied the structure, drawn to Mannar by the pearl banks offshore.