Historian Richard Felix is holding an overnight vigil in Greyfriars Kirkyard in a bid to find out more about the ghost of 17th-century nobleman Sir George Mackenzie, which is said to haunt the graveyard's Covenanters Prison.
Thirty volunteers will spend a couple of hours in the tombs of Edinburgh's oldest surviving burial place armed with monitoring equipment to try and learn more about its paranormal activity.
For decades visitors to the prison have claimed they have been left with scratches, welt marks, bruises and feelings of nausea, with some saying they have been knocked to the ground.
Those taking part in the vigil will be split into small groups and given a range of recording devices - such as tape recorders and thermometers - to try and gather more evidence about "Bloody" MacKenzie.
Mackenzie was the King's Advocate who put thousands of Covenanters to their deaths at the tiny prison.
Mr Felix said it was the first time he had led a vigil in Edinburgh and hoped he would get a mix of paranormal fans and sceptics along to the one-off event.
He said: "I have done over 115 programmes now for Most Haunted, so I have seen a few scary places in my time, but there is nothing like the Covenanters Prison.
"I would say it was arguably the most haunted place in the UK and this will be a great opportunity to spend a bit of time in there and try and learn a little bit more about what on earth is going on.
"I will try and give people a bit of the history of the place but it will be quite an active process with the groups helping me conduct more research about the tombs.
"We've only got a couple of hours but I am sure we'll be able to make some progress and the odds are pretty high that we'll see some sort of activity."
A spokesman for City of the Dead Ghost Tours, which runs daily tours of Greyfriars Kirkyard, said the Covenanters Prison was awash with paranormal activity.
He said: "It is going to pretty scary for Richard and his group because the prison has the most amount of recorded paranormal activity in the UK.
"It will be quite an adventure and I'm sure there will one or two scares over the course of the vigil."
The Covenanters vigil will start at around 1.30am on Thursday and lasts for around two hours.
Greyfriars Kirkyard is visited by an estimated 15,000 people every year with about ten times that number coming into the graveyard, many of them tourists visiting the Greyfriars Bobby memorial.
Mr Felix has just published his new book, The Ghost Tour of Great Britain: Scotland, which features more than a dozen supposedly haunted sites in the city.
Mr Felix will be doing a book signing at WH Smith at Cameron Toll and Blackwells Bookshop on South Bridge on Wednesday. Tickets for the Greyfriars vigil are available from the Tron Centre on the High Street.