In 1453, when the Ottoman Empire captured Constantinople, Sultan Mehmed II ordered some changes to the city’s eastern Orthodox cathedral, the Hagia Sophia: the altar was swapped out for a minbar, the platform from which the imam addresses the congregation; and four slender minarets were added, among other things. For nearly 500 years the Hagia Sophia was a mosque, becoming, in 1931, a secular museum that enchantingly reveals layers of religious history, art, and architecture.  Today the purple porphyry marble from Egypt glows richly; the Byzantine golden dome displays Islamic geometric adornments; and mosaics of the Virgin Mary sparkle up high. To better show off its wonders, the museum’s upper gallery hosts a permanent exhibition of images by Turkish architectural photographer Ahmet Ertug. In these carefully lit photos, the tiny tiles of the Virgin’s face and robes can be easily discerned. A museum within the museum.