Thalassery Fort is the town's clearest landmark: a laterite British East India Company fort above the old harbour, built when Tellicherry was a pepper-trade stronghold. The walls are compact, but the setting is excellent, with sea air, old colonial geometry, and the town pressing in around it.
It works best as a starting point. From here you can walk toward the pier and Overbury's Folly, then turn back into the old streets for the mosque and temples.