St Sophia, the most influential church of Byzantium. Originally built by Emperor Constantine in the 4th century, reconstructed by Emperor Justinian in 6th century and converted into a mosque by the Ottomans in the 15th century, it still stands today as one of the world's greatest architectural marvels. The magnificent interior is testament to the unique east-west synthesis that is manifest in Istanbul. Shimmering biblical mosaics juxtapose huge plaques bearing the names of Islamic caliphs.
Blue Mosque, another of the world's most important religious buildings. Built in the 16th century the mosque is unique for it's 6 minarets and it's celestial interior decorated with the famous blue Iznik tiles.
The Hippodrome, scene of chariot races. Although little remains of the great stadium which, in its hey day it is thought to have held 100'000 people, the Obelisk of Theodosius, the Serpentine Column and the Column of Constantine are highlights.
Topkapi Palace, residence of Ottoman Sultan's from the 15th to the 19th century. With its impressive treasury, exquisite harem, attractive courtyards and pavilions housing huge collections of antiquities, Topkapi Palace offers a true insight into the heart of the Ottoman Empire.
The Grand Bazaar, was the commercial heart of the old city and its 4,000 shops are full of treasures  including carpets and kilims, silks, jewelry, ceramics, icons, and leather goods. Wandering through the Grand Bazaar, indulge in some shopping, Ottoman style.