The tour began with the usual health and safety checks – plus one I'd never heard before. Visitors should be aware that there are stairs, enclosed spaces, a moment of complete darkness, and that anyone who is particularly spiritually sensitive might become distressed.

We were descending into the dungeons of Norwich Castle and guide Jeff Wood said he always gives the spiritual warning because some people are convinced they are picking up the terror of past prisoners.

There are said to be ghosts down here, and deep beneath the castle, where people were held in total darkness for months, chained to walls and tortured, it is easy to believe something of the unspeakable horror of the past might live on.

Although these vast stone vaults were built as storerooms for the Norman castle and royal palace, by 1345 they were part of the city gaol and for 500 years they held the very poorest prisoners who could not afford to buy themselves the privilege of daylight, or a dungeon not running with excrement and disease.

The tour begins in a room lined with shackles, chains, stocks, a whipping post, a ducking stool and a gibbet. These were real instruments of torture and death, used on real people and the room is already unsettling, even before Jeff launches into specific stories. Then he introduces the death masks. These models of the heads of hanged men are so detailed they show every feature of the faces, including the rope marks around elongated necks.

There are happier stories. A model of Henry Kable sits in a dungeon. He was sentenced to death but was eventually transported to Australia, where he is said to have been the first English settler ashore. He met his wife, Susannah, also under sentence of death, in Norwich Castle prison, but the couple went on to highly successful lives in Australia and their 10 children were the first of many thousands of descendents.

Tour guide Jeff said he loves welcoming visitors who have traced their family history back to Henry Kable or a fellow Norwich prisoner. He used to be a Heathrow aeroplane fitter but moved up to Norfolk with his wife to be close to their grandchildren. Now he is an expert on the history of Norwich Castle, from the depths of its sinister dungeons to the battlements towering 124 feet above ground level.

On a clear day you can see the ridge of hills along the North Norfolk coast. In the past the battlements would have overlooked the gallows on the Castle bridge, where thousands flocked to see public executions.

'Gallows days are where our phrase gala day comes from,' explained Jeff.

Today the battlements tour is much more uplifting. 'I love coming up here every single time. There is so much to see,' he said, as he surveyed the fantastic cityscape below, and countryside beyond, and began illuminating the high points of 2,000 years of human history.

Norwich Castle has daily dungeon and battlement tours , �2.10 (�1.80 cons), �1.50 children, 01603 495897, www.museums.norfolk.gov.uk