The Blue Mosque or Sultan Ahmet Mosque
This mosque is ENORMOUS. At night, you can hear the call to prayer from the 8 minarets. You can hear the call throughout the city coming from any of the 2,800 mosques. Inside the mosque, everyone must cover their shoulders and legs, take off their shoes, and women must cover their heads. The mosque, though cavernous, is warm and welcoming, almost cozy.