Within the same concept of Arab-Norman style, as seen in the Palazzo dei Normanni & Cappella Palatina, going to Monreale is an absolute must-visit.
The Duomo, a second Cathedral less than 10km from the city centre one, was built initially when the Bishop had to flee from the Arab invasion. Then, as we have seen, things got way friendlier between Arabs and Christians, and both the Cattedrale di Palermo and the Duomo di Monreale were built in mixed style. Only, the Monreale one had the chance not to be redecorated by tasteless kitsch artists in the 1700 and still bears its original style.
For those who have visited the Cappella Palatina, the experience will be similar, only in a way larger size: Byzantine mosaics, lots of gold, marble, a Pantokrator Christ that simply does not takes his eyes off you, wherever you try to hide, precious wooden ceilings.
After the Duomo, the visit of the Chiostro (cloister) on its right side also is mandatory. I personally prefer another cloister in Palermo, San Giovanni degli Eremiti’s one (more on that further on), but this also is a masterpiece that deserves a visit.
Getting to Monreale can be tricky, as Google Maps can show you – with traffic, you should count more or less one hour from your hotel in the centre. So don’t consider going the other way round – staying in Monreale (a few very cute bed&breakfasts would be available) and come to the centre for the wedding – it would not be practical. For the adventurous, bus #389 goes from piazza Indipendenza (i.e. Palazzo dei Normanni) to the Duomo di Monreale.