Monreale's cathedral, built by William II, dates to 1172 and is now part of a larger UNESCO World Heritage Site that also encompasses the Royal Palace and the Palermo Cathedral, among other sites. Designed by Islamic architects, the cathedral's walls are filled with gilded mosaics depicting Old Testament events, the life of Jesus Christ and the life of the apostles. There's also a Benedictine cloister on site with a courtyard and garden built during the same time period.

Visitors say the duomo is stunning and recommend visiting the cloister. They also suggest allowing a day to see both.

The cathedral is located less than 10 miles west of Palermo. It is open Monday through Friday from 8:30 a.m. to 12:45 p.m. and from 2:30 to 4:30 p.m., and tickets cost 4 euros (about $4.50) for those 4 and older. Visitors also need to be "decently" dressed. For more information, visit the Duomo website (in Italian).