THE Athens of the north or auld reekie? Take your pick. Edinburgh is a Jekyll and Hyde city.

It was a bastion of the Enlightenment, an important centre of philosophy and medicine, where gifted men made important discoveries amid spectacular architecture.

It was also a den of iniquity; a place of slums, poverty, disease, murder, public executions, body-snatching and a fickle mob baying for blood at the slightest provocation.

The theme of my visit was Halloween, so Edinburgh's role in the advancement of economics, philosophy and medicine took a back seat to its darker side.

I was not looking for the Athens of the north; rather I wanted to probe the depths of auld reekie.

I wanted to go underground and find out how criminals supplied eminent surgeons with dead meat for the scalpel.

A good place to start was the Ghosthunter Trail run by Mercat Tours. We met at 9.30pm, beside the Mercat Cross, a substantial eight-sided monument next to St Giles Cathedral on the Royal Mile.

Gary Shiells, our caped guide with flaming red hair and beard, regaled us with a bloody tale of regicide that possibly inspired William Shakespeare to write his "Scottish play" (or Macbeth to the less superstitious among us).

It involved a powerful noble who coveted the crown; a prophecy by three hags on a blasted heath; the stabbing to death of the King of Scotland; and his vengeful widow's dreadful revenge.

The nobleman was tortured, surrounded by a mob baying for blood, for three days on the streets of Edinburgh before being put out of his misery and executed.

I played the unfortunate monarch in Gary's exuberant re-enactment and took a blade in the chest. Fortunately, it was retractable and made out of plastic.

It was time to go underground. Gary set the scene: "A great bridge is built spanning a deep valley to the south of the Royal Mile. Under its 19 enormous arches, in a catacomb of underground chambers, a community begins to thrive. Trades, first legal and then illicit, flourish."

The underground vaults were created in the late 18th century, abandoned by the 1830s - and only opened again to the public in 1994.

Walking down the stone steps you could almost taste the malice and misery as you entered the hidden abodes of crooks, cut-throats and conmen. Every vice known to humankind was practised here with alarming regularity, amid the stench and filth of disease-ridden poverty.

Inside the vaults, you could get away with murder because the city's law-enforcers were too scared to enter. Body-snatchers would store their corpses there, until the surgeons were ready to receive them. Wealthy philanderers ventured into the dimly-lit vaults looking to sate their appetites.

Gary told us of a spectre named Boots because it wears footwear beloved of cavalrymen.

The pock-marked Boots guards its hidden cache of human bones with relish.

According to Gary, a woman on the Ghosthunter Trail was "thrown" several feet across a vault as the ghostly Boots "possessed" her body for a few seconds. She emerged from her ordeal physically unscathed.

Above ground again, we walked to the eerie Canongate Cemetery, off the Royal Mile. Historians believe at least one-third of its graves were robbed to meet the demand for cadavers from medical students and their tutors.

A well-drilled team of grave-robbers could carry away a naked corpse in a sack within two hours of the first sod being cut. One kept a look-out, while two others dug out the body, using a wooden spade to keep the noise down.

They usually worked from 4pm, when it got dark, to 6pm, when the watchman came on duty.

If caught, the punishment dished out depended on whether the corpse was naked or clothed. If naked, the grave-robbers would be sentenced to a week in jail for desecration. If clothed, the grave-robbers would either be deported to Australia or hanged for theft.

As the city clock chimed the hours at 11pm, Gary bade us a safe journey home, before walking into the mist that shrouded the Royal Mile, his footsteps echoing on the ancient stones.

Edinburgh's Christmas festivities kick off on the Thursday, November 23, when the festive lights will be turned on, the 30-metre high Edinburgh Wheel starts turning, the ice-rink welcomes skaters, the carousel starts spinning and the German and Christmas markets begin trading.

Fact file

Accommodation: Richard spent two nights (bed, breakfast and dinner) at the Best Western Bruntsfield Hotel, 69 Bruntsfield Place, Edinburgh EH10 4HH. Tel: 0131 229 1393.

Website: www.bw-bruntsfieldhotel.co.uk

Getting there: Richard travelled between Edinburgh and York courtesy of GNERWebsite: www.gner.co.ukCity tour: Mercat Tours Ltd, 28 Blair Street, Edinburgh EH1 1QR. Tel: 0131 225 5445.

Website: www.mercattours.com