Duomo di Monreale

Monreale is located southwest of Palermo, and its duomo (pictured above, view of the facade) is one of several points of interest in the town. The interior of the church is decorated with beautiful mosaics so you simply must stop in and have a look. Generally, churches charge a small fee to enter, but when there is a wedding going on, they do not enforce this. Also, the cloisters are worth exploring as well!  The tower is open, but there's a fee for that, too.  It's great if you want some aerial shots of the cloisters and the surrounding countryside.