The Barnton Quarry base, which is undergoing restoration, was built in the 1950s during the Cold War – and remained a secret until the 1980s.
Deep underground beneath Corstorphine Hill, near Edinburgh, it served as Sector Operations Centre for co-ordinating RAF fighter jets, and aimed to protect Scotland from attack by Russian long-range nuclear bombers until around 1960.
It was used as a control centre where information was analysed, and became a base for a radar air defence system.
Later it was reconfigured to become a regional seat of government in the event of a nuclear attack, designed to accommodate 400 politicians and civil servants for up to 30 days.
But in the 1990s it fell victim to vandals, who torched it and raided the interior for scrap metal.
It was built over three floors, which included an operations room with two storeys.
The bunker will be open to the public during the weekend of September 29 - 30 as part of Doors Open Day.