Spring (April-May) and autumn (September-October) are the best times — comfortable temperatures, lower crowds, and the surrounding Umbrian countryside at its most beautiful. Summer is hot and the Duomo piazza can get very crowded with tour groups; arrive early (the cathedral opens at 9am) to beat them. In June the town hosts Corpus Domini, a medieval pageant commemorating the Miracle of Bolsena, with processions in historical costume.
December and early January see the Umbria Jazz Winter festival, which draws international jazz musicians to the town's theatres and churches. The town itself is quiet and atmospheric in winter, with morning mist over the valley and lower prices throughout.