The old town is still ringed on three sides by the heavy bastioned walls the Spanish put up in the 16th century, when Orbetello became the capital of the Stato dei Presidi. The fortifications follow the shoreline and are best appreciated from the lungomare on the lagoon side, where the curtain wall drops straight into the water.
The Polveriera Guzman, a former gunpowder magazine just outside the walls on the eastern side, is now a small archaeological museum displaying Etruscan and Roman finds from the Maremma. It is more interesting for the building itself — vaulted brick chambers that have hardly changed since the 17th century — than for the collection.