Whitehall was a road in Westminster.
Sherlock Holmes and John Watson walked along it on their way to their lodgings at Baker Street. (PROSE: All-Consuming Fire)
In the 1960s, a secret bunker was built under Whitehall. This was later used by members of Operation Golden Age as their base. (TV: Invasion of the Dinosaurs)
A number of British government offices were located there, including that of the Home Secretary, the Ministry of Defence, and the Forge. As a result, "Whitehall" was slang for the government departments and civil service. (PROSE: The Dying Days, Project Valhalla)