Holy Rosary Church is one of Thalassery's old Christian landmarks, with roots commonly traced to the 16th century. Its Gothic details and stained-glass work give it a different texture from the town's fort, mosque, and temple sights.
The church is close enough to Thalassery Fort and the seafront to include on a compact heritage walk. Go for the building and the coastal Catholic history rather than expecting a large museum-style visit.