The Castle of Silves is the most complete surviving Moorish castle in Portugal, its red sandstone towers and walls rising above the orange groves with a grandeur that hints at the city this once was. Built progressively from the eighth century onward on the site of an earlier Iron Age hillfort, the castle enclosed the Moorish medina that made Silves one of the major urban centres of the Iberian peninsula during the Islamic period.
Admission gives you access to the entire castle interior and the battlements circuit. The walls are in excellent condition — you can walk almost the full perimeter, with good views in all directions across the Arade valley and the distant hills toward the coast. Inside the walls are the remains of the old cisterns, a few excavated foundations, and an external moat now used as an archaeological garden. In summer there are sometimes temporary exhibitions and events in the courtyard.
The castle is directly adjacent to the cathedral and the two can be visited in a single circuit of about ninety minutes. If you only have time for one thing in Silves, this is it.