The Rocca Maggiore is the great fortress that crowns the hill above Assisi, visible from almost anywhere in town. The current structure dates largely from 1367, when Cardinal Albornoz rebuilt an earlier castle that had been destroyed by the townspeople a century before. It is bare and military rather than residential — long corridors, small dark chambers, and a circular keep with arrow slits.
Climb the round tower for the best view in Assisi: the whole town below, the Basilica di San Francesco, the Umbrian plain stretching toward Perugia, and Monte Subasio behind. The walk up is steep and the inside is unheated, so this is a clear-weather and proper-shoes attraction. Allow about an hour.