This cylindrical stone tower has watched over the Golden Horn since 1348, when Genoese merchants built it as the apex of their fortified colony. Climb to the top for a 360-degree panorama that takes in the minarets of Sultanahmet, the Bosphorus shipping lanes, and the sprawl of the Asian shore. At sunset, when the muezzins of a hundred mosques begin their call in sequence, it's one of Istanbul's most magical moments.