The abbey dominates the upper end of town and is the reason most travellers come. A Benedictine foundation traditionally dated to the 11th century (on much older Lombard or Greek-rite foundations), it was rebuilt and expanded through the late Middle Ages and reached its current scale in the 16th and 17th centuries, when the order was at its wealthiest.
Two cloisters survive — a sober Renaissance one and a more elaborate later cloister with a wellhead at its centre — along with the abbey church, the refectory, the chapter house, and a remarkable cycle of late-Mannerist frescoes in the corridors. The complex was suppressed in 1809 and spent the 20th century in slow decay before a long restoration brought it back as a museum and cultural centre. Visits are guided; check opening hours, which are irregular outside summer.