The Mosque of ibn Tulun is perhaps Cairo´s most imposing. It sits on a hill not far from the citadel and has wonderful views. You can look across the expanse of the city and make out the shapes of the Pyramids through the haze on the opposite side. Mosques are always interesting to visit as they play a central role in the lives of muslims. It´s great to sit and watch people as they come and go.