Castello is the medieval hilltop citadel at the heart of old Cagliari, ringed by honey-coloured Pisan limestone fortifications that still largely stand. Built from the 13th century onward by the Pisans and subsequently controlled by the Aragonese and Spanish, the quarter sits on a flat-topped hill with commanding views in all directions — north over the modern city, south over the port and the Gulf of Angels, east toward the salt lagoons.
Within the walls, the streets are narrow and mostly residential, with the cathedral, the two Pisan towers, and the National Archaeological Museum clustered together at the summit. The neighbourhood is quieter than the lower districts in terms of restaurants and bars — most visitors come to see the monuments and then descend to eat — but in the evening the bastions and terraces fill with locals watching the sunset over the bay.