Never on a Monday
Not just in Perugia...many (perhaps most) Italian museums are closed on Mondays. This can be a spirit-killer if you're only in a city or town for a single day and the museums are unavailable, which is why the Spirit moves me to suggest that much of Italy's great art is found in its churches, virtually all of which are open every day of the week (and are generally free, to boot). So find your Caravaggios and della Robbias in the local duomo, and soak in the notion that people have been hallowing with their prayers the place where they are situated for many hundreds of years.


Cat on a hot wooden windowsill
Chiesa di San Francesco