Istanbul

Constantinople was a city located on Earth, in Turkey.

In the 3rd century, the Doctor encountered Fenric in Constantinople, where he defeated him at chess and trapped him in a flask. (DW: The Curse of Fenric)

During another visit (or possibly the same one), the Doctor bought a hookah, which he would later use as part of a ruse to evade the Chancellery Guard on Gallifrey. (DW: The Deadly Assassin)

In 1914, the Doctor and Ace visited Constantinople to locate and dispose of a malfunctioning Krivani interstellar drive. (ST: Ante Bellum)

Constantinople was later renamed Istanbul. (NA: Shadowmind)