We would hate to imagine Palermo without this masterpiece of Arab-Norman architecture. This decadent site is not only fantastic for Instagramming some ruin porn, it also helps you get an idea of the fascinating historical currents that have shaped Palermo. This once vibrant place of worship was built in the middle of the first millennium as a church, and in the 10th century converted into a mosque when the island was under Muslim rule and converted into a monastery at the beginning of the second millennium. While you won't find hermits in the cloister, you will find wonderful citrus trees among other eye catching vegetation.