Hagia Sophia - Istanbul. Not a cathedral, in fact a Mosque. But it used to a church, an early and important one, when the city was called Constaninople and was the seat of the Roman Empire.
Istanbul,Turkey~No shoes allowed in the Blue Mosque or any mosque for that matter. Women must cover their legs and shoulders when entering the holy mosques. The Muslims practice Islam and its five Pillars. One of the pillars is to pray five times a day. Prayers can be heard over the entire country from loudspeakers coming from these beautiful mosques.