Istanbul, Turkey

Istanbul is the only city in the world that spans two continents and three great civilisational traditions — Byzantine, Ottoman, and modern — each leaving an extraordinary architectural legacy. Hagia Sophia's 537 AD dome still astonishes engineers; Sinan's Suleymaniye Mosque (1557) is one of the world's greatest buildings; and contemporary Turkish architects are adding striking new chapters to a 2,700-year story.