One day
Start by walking a stretch of the star ramparts and the bastions for the shape and the views, then explore the whitewashed old town — the Praça da República, the former cathedral, the tiled octagonal Church of the Consolation and the castle. See the great Amoreira Aqueduct on the edge of town, have an Alentejo lunch with a local red, and drive up to the Forte da Graça and the Forte de Santa Luzia in the afternoon for the forts and the plains views. Buy some candied plums before you leave.