Timbuktu was a city in Mali, on the African continent on Earth.
Timbuktu was suggested by Captain Jason Nyere of the CSS Delphinus as a possible destination after departing the Byrd Research Complex and evading AeroNav detection with two stranded Vulcans. (TOS novel: Strangers from the Sky)
Vic Fontaine once commented that he thought Felix would have sold copies of his holographic program "halfway to Timbuktu and back again". (DS9 - Millennium novel: Inferno)