Photographs of renovation work at the Queen Anne building within the castle have captured hazy mysterious blue orbs floating above the builders’ heads. Many of the workers on the site now have refused to be left alone while working, while Paul McDevitt, of Mansell Builders, has called in a medium to shed some light on the mystery.
He said: "A medium spent the night here and told us she felt the presence of two women and one man in the room.
"We have been working here since last November and have recorded our progress every week using a digital camera. But last week, we noticed ghostly blue orbs in our pictures. Strangely the orbs only appear in one picture per roll of film.
"In all my time spent working on historic projects like this I have never seen anything like it," he added.
Some of the workers have requested a special canopy to shield them from the glare of ghostly eyes gazing down on them.
Willie Hamilton, the site manager, said: "I can feel a presence whenever I am alone in the site office. It is as if someone is above me, looking down as I work. It is very spooky."
Beneath the room - which the builders are converting into a function suite - are cramped vaults where many prisoners from the Napoleonic Wars died horrible deaths.
Simon Steel, the site foreman, said: "The builders say they don’t like being left on their own - but I think they are just feart."
Edinburgh Castle is reputed to be one of the most haunted spots in Scotland. Visitors have reported phantom pipers, headless drummers and even a ghost dog.
Yet paranormal investigators, who launched what was described as the world’s largest ghost hunt at the castle two years ago failed to find scientific evidence of spirit activity.