Salem Fort is the oldest surviving structure in the city, built by Hyder Ali of Mysore in the latter half of the 18th century. What remains today is fragmentary — sections of the outer wall and some ruined bastions — but the site gives a sense of the city's history as a contested frontier between the Mysore sultanate and the Carnatic region.
The fort area sits near Fort Road in the centre of the city, close to the District Collectorate. There is no formal entrance fee or organised tour — you walk around the remains, which are embedded in the fabric of the busy town. Christ Church (1867), a colonial-era Protestant church on the same road, is worth a look as you pass; it is a modest but well-preserved example of South Indian colonial ecclesiastical architecture.