This nuclear bunker is under the Corstorphine Hill, embedded in the Barnton Quarry. It was built in 1952 as a Cold War shelter for the British government and the Queen, should she happen to be at her Edinburgh residence. It was even outfitted with a broadcast room for the BBC.
The Soviet nuclear attack on Scotland never came, and thus the bunker was never used. It was a secret until 1963 when a group called Spies for Peace exposed it to the public. It was purchased in 2005 by a private owner who intends to turn it into a museum, although the bunker has long been explored by intrepid spelunkers. (Warning: due to two fires, it is full of asbestos.)