Buried beneath Edinburgh's Royal Mile that runs from the castle down to the Palace of Holyrood House lie the remnants of a clutch of streets and houses that dates back to the 1600s.
On a typical day, the only visitors are those on historical tours.
But last night, with the help of 200 locals, the site was to be turned into a giant scientific experiment.
The man behind the experiment is a one-time magician and now psychologist, Richard Wiseman of the University of Hertfordshire.
The aim of the experiment, he says, is to investigate just why it is that people report ghostly experiences in "creepy" buildings.
volunteers
From 10pm until midnight, small groups of volunteers will be allowed to venture inside the buried homes.
When they emerge, they will be asked if they saw or felt anything strange in any of the rooms.
They will also be quizzed on what kinds of ghosts, if any, they can imagine occupying different locations.
"What's fascinating about this site is that people see things, they see people, and often the same figures are seen in the same locations by different people," Wiseman said.
For the past month, his team has rigged the underground site with sensors that are capable of detecting tiny changes in temperature, humidity, local variations in magnetic field and soundwaves of such low frequency that they are inaudible to the human ear.
STRANGE EXPERIENCES
They hope their readings will go at least some way to explaining any strange experiences the volunteers report.
"With luck we will get people reporting experiences in the same places that have a reputation for being haunted, and hopefully we will be able to link them to temperature or whatever," Wiseman said.
"We already know that there looks to be something very different about the ghost sites," he said.
The experiment, which runs each night until Tuesday, will also check whether certain rooms and environments make people more likely to report similar apparitions.
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