Istanbul Old City
The dome of Hagia Sophia, Istanbul. Photo via Wikimedia Commons.
Sultanahmet is the historic peninsula where Byzantium became Constantinople became Istanbul: Hagia Sophia, the Blue Mosque, Topkapı Palace and the Basilica Cistern within a few hundred metres of each other.
This is the densest concentration of world heritage in Turkey. Two full days is the minimum; the museums alone could fill a third.
