Photo: Wikimedia CommonsFounded in the tenth century, Al-Azhar is one of the oldest mosques in the world and the seat of one of the most important centres of learning in Sunni Islam, a serene courtyard of pale arcades and minarets in the middle of Islamic Cairo. Visitors are welcome outside prayer times. Dress modestly and remove your shoes, sit a while in the vast marble courtyard, and climb a minaret if the guardians offer for a rooftop view.