Turkey - Istanbul - Hagia Sophia (Ayasofya)

When the Christian Emperor Justinian inaugurated Hagia Sophia, meaning Church of Divine Wisdom, in the year AD 537, it was the most impressive building in the world and remained the crowning achievement of the Byzantine Empire for over a millennium. In the 15th century, Mehmet the Conqueror converted it from a Christian church to a mosque, adding the minarets, tombs and fountains. Turkey became a secular republic in 1923 and Hagia Sophia was established as a museum 12 years later. Designed to represent the heavens, visitors marvel at the huge 56m (183ft) high dome. Other highlights include Byzantine mosaics and huge Ottoman circular shields containing calligraphy of Koranic verses.