For years this mysterious sphere frequently turned heads and prompted confused expressions from motorists heading to and from the north Norfolk coast.
Most people who drove past it had no idea about the crucial role it played in defeating the Nazis.
Now, after seven years of hard work and fund-raising, the story of the Langham Dome is becoming more widely known.
The dome, at Langham near Wells, was built in 1942 and was a training base for anti-aircraft gunners.
It was one of 40 built across the country.
There are now just six in existence.
The Friends of Langham Dome, a voluntary group, spent seven years transforming the building into a visitor attraction, telling the dome's history.
On Saturday they held their first open day since the dome opened to the public in 2014.
The Langham Dome used what was at the time cutting edge technology to train ground to air gunners.
Servicemen from the UK, Australia and New Zealand trained inside and images of aircraft would be projected onto the walls.
The spherical shape would enable them to simulate firing at aircraft from all angles.
The gunners would then be trained in firing live ammunition at nearby Weybourne and Stiffkey.
Patrick Allen, chairman of the Friends of Langham Dome, said: 'It has taken a lot of work but we're pleased with how things have turned out and the feedback from the public has been really positive.
'We've even had a visitor from Australia whose parents met here during the war.
'This is a living memorial to those who served here and paid the ultimate sacrifice, a visitor attraction, a place of pilgrimage for relatives of those who were here and an educational resource, with many schools visiting to learn the story of the Langham Dome.'
The Friends of Langham Dome raised approximately £750,000 for the project with money from Heritage Lottery, English Heritage and local charities and fund-raising.
Mr Allen said: 'Our Heritage Lottery funding runs out at the end of the year, so we need to raise our profile so we can cover our running costs and develop the dome further.'
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