This once-mighty fort is now home to administrative offices, and though large sections of the structure are crumbling it's still an evocative sight. It was built by the Portuguese in 1628, but the Dutch took over after just 10 years, followed by the British. Inside the courtyard are some dishevelled yet colonnaded old colonial buildings. Look for English canons, surviving watchtowers and a ruined bell tower. Views across the lagoon are magnificent.
There's a tiny museum with several intriguing items labelled, alas, only in Tamil and you can glimpse the old jail (now a store).