Singapore

The Doctor attempted to to deliver his companion, Charley Pollard to a rendezvous there in 1930, but ended up in Manhattan. (BFA: Invaders from Mars, Seasons of Fear)

Major General Scobie, as a British Army officer, was posted to Singapore in the 1950s. (MA: The Scales of Injustice)

Behind the scenes
Singapore was supposed to be the primary location for the aborted Doctor Who story Yellow Fever and How to Cure It.