Mount Everest was a mountain.
Everest stood at around 8km tall. (TV: The Waters of Mars)
In 1953, the first humans successfully climbed Mount Everest. (TV: The Idiot's Lantern)
Santiago Jones visited it during one of his journeys. (TV: Death of the Doctor)
When the Earth nearly became an ocean planet in the early 22nd century, much of Mt Everest was submerged in water. River Song recalled once fishing off the coast of Everest. (AUDIO: Kings of Infinite Space)
At some point during the 51st century, the Doctor helped carry the Mona Lisa up Mount Everest on a camel to preserve it from a war. (PROSE: The Art of Destruction)