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)

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)