1-Sultanahmet Square: The old centre of the world.
Before Greenwich was accepted as the prime meridian, the centre was accepted to be the Milliarium Aureum which was in Rome. The column Milliarium Aureum was accepted as the point from which all the principal roads of Rome diverged.
When the capital was moved to Constantinople, the Milion Monument was considered as the Byzantine zero-mile marker, the starting-place for the measurement of distances for all the roads leading to the cities of the Byzantine Empire. The monument was built by Constantine the great who is the founder of the city.
2- Hagia Sophia
As one of the most important symbols of Istanbul, Hagia Sophia is a must see. The building has served as a church during the Byzantine era, a mosque during the Ottoman Empire and today it opens its doors to guests as a museum.
3-The Horse Market
4- Basilica Cistern
The Basilica Cistern is the largest of all ancient cisterns that lie beneath Istanbul. The cistern was built by Emperor Justinian and is the largest surviving Byzantine cistern.
If you are a Dan Brown fan, you might recall the cistern from his book Inferno.
5- St. George’s Cathedral
The Church of St. George is not exactly famous for its architecture; however, it does reflect all the opulence and beauty of an Orthodox church.
The church is popular with its artefacts and relics, which include: the patriarchal throne, believed to date back to the 5th century; the tombs of three female saints; three rare mosaic icons and most importantly the Column of Flagellation to which Jesus was tied and whipped.