Mainfranken Theater is Würzburg's main performing-arts house, covering opera, theatre, dance, and concerts. It gives the city an evening option beyond wine taverns and baroque sightseeing, especially useful if you are staying overnight rather than passing through for the Residence.
Check the current venue and schedule before booking, as German theatres often run multiple stages or temporary arrangements during renovation periods. For travellers with some German, it can be a rewarding local night out; for everyone else, opera, ballet, and concerts are the easiest entries.