A few steps from the Hagia Sophia in Sultanahmet sprawls the so-called Blue Mosque, a monumental structure of curved stone walls, 13 domes and six slim minarets piercing the sky. Built in 1616 by Sultan Ahmet I, it has the largest courtyard of all Ottoman mosques. Inside, the massive walls and high domes are ornately decorated, pierced with hundreds of windows and clothed in colourful tiles – many of which feature floral designs and some of which are indeed blue. As it is a working mosque, the building is closed to visitors during prayer times.