The Bunker has a modern entrance following a 'Cold War' upgrade in 1988
The Bunker, which was built in 1941 for the RAF in Inverness, will be open to the public for Doors Open Day on Saturday.
The building, along with two other bunkers nearby which are both now demolished, played a vital defence role in the Highlands during World War II.
Information from radar stations on the Scottish coast and in Northern England was processed inside the Bunker.
It was dubbed the filter block and acted as the collecting point for radar plotting information with a range of 180 miles from the Scottish coast.
Secrecy was paramount as staff dealt with the location of Luftwaffe bombers. Personnel were denied access to areas in the building other than those they worked in and were never permitted to talk about their work.
How the filter room would have looked during World War II
The nerve centre of the filter block was the filter room, which was manned round the clock by staff known as filter plotters.
Each member of staff was linked to one or more radar stations via a telephone and headphones and they would mark out the position of aircraft on a map.
The filter block closed in March 1946 when all radar stations in Scotland were ordered to stop reporting.
The Bunker was used for RAF training purposes in the post-war period. In 1958 the Civil Defence Corps moved into the building, leaving the Bunker in 1968.
As the Cold War took grip in the early 1980s, the Bunker was designated as the Highland Regional Council's emergency centre.
From here it was thought officials would organise the recovery of the area if a nuclear attack took place.
The Bunker was strengthened for this task. Blast and sealed doors were added to the front entrance and new generators and ventilation system were fitted.
As the work was completed, the Cold War came to an end.
Most bunkers in the UK have been sold off or left to rot - but the Inverness Bunker still serves as an emergency centre for the local population.
Andrew Denovan, emergency planning officer at Highland Council, said: "The emergency centre is a category B-listed building because of its historic significance. It is amazing to think that it once played such an important role in the defence of the country.
"Throughout the years it served in some way to safeguard the people of the Highlands.
"Like so many other buildings participating in Doors Open Day, it has a story to tell about the fate and fortune of the generations before us."