Few would disagree that unlocking Oxford’s grim, grey prison in 2006, and opening up the castle in which it was housed, has proved one of the great planning success stories of recent years.

For decades before the transformation of that part of Oxford just west of the city centre, containing the oldest monument in the shape of the Saxon Mound, and possibly England’s oldest standing secular building, St George’s Tower, those inhabitants of Oxford who were not residing behind bars at Her Majesty’s pleasure hurried past the glowering old place.

They knew little of the goings-on behind those walls where so many executions had taken place — and most did not want to.

Then, suddenly, a whole new — but at the same time old and historic — area of Oxford appeared before our eyes and, as a direct result, the company which runs the new heritage site carried off the Hospitality and Leisure category at the Oxfordshire Business Awards last year.

Emily Hirons, visitor centre manager of Oxford Castle Unlocked, who is in charge of day-to-day running of the Castle Yard, St George’s Tower, the Mound, Debtors’ Tower, and the old D Wing of the prison, said: “Winning the award was great for us. It was wonderful to receive recognition locally and from our peers.

“And forming new links with local businesses, for example the sponsor of the award, the Four Pillars Hotel, has proved very useful in helping us to manage the success of this enterprise which has been well above expectations.”

The £6m heritage side of the five-acre former prison site was originally created by the Oxford Preservation Society with the help of £4m from the Heritage Lottery Fund, £1.5m in work provided by developer Trevor Osborne, and £500,000 introduced through the Preservation Society’s fundraising efforts.

The heritage venture occupies about a third of the total. The rest houses the Malmaison Hotel, the Living Room, and various other restaurants and bars.

In 2007, the first full year that Oxford Castle Heritage Projects operated Oxford Unlocked, there were 18 staff and 45,000 visits to the attraction. Now there are 25 employees and last year there were 70,000 visits, producing a turnover of about £650,000.

Oxford Castle Heritage Projects is the commercial manager of Unlocked, part of the Continuum Group that runs attractions from Edinburgh to Portsmouth.

A full education programme runs from the Castle’s Key Learning Centre in partnership with Oxfordshire County Council which funds a full-time learning and access officer.

Ms Hirons said: “Now our problem, if you can call it that, is how to manage our success. Last August, for example, we reached capacity in terms of visits, so now we are introducing new schemes such as early opening for language school groups.

“We are also introducing site-wide tours because we have noticed so many people are still confused by the division between the hotel side of things and the castle side.

“It’s still surprising how many people say they have never visited the castle.”

She added that during February half-term about 90 per cent of visitors were local but that nevertheless the castle still needs to attract more local people year round.

Ms Hirons said: “Despite the trend towards ‘staycations’ — people staying at home for holidays instead of going away — it is still surprising how many never look at what is on their doorstep.”

Debbie Dance of the Oxford Preservation Trust joined the discussion.

She said: “Opening the castle has made people much more aware of the history of Oxford before the university, a whole new area waiting to be explored.”

That early history, stretching back more than 1,000 years, becomes apparent when you climb the mound and look over the city’s “dreaming spires” from a new angle.

From here Robert D’Oilly, the Norman baron who built the castle in 1071 could overlook the district in which Oxford was developing. He was charged with the task of building the castle to oust the English from their regional bases.

And that exploration is now open to the business community, as Ms Hirons explained.

“As part of our three-year review we are aiming at the corporate market. For instance, there is the possibility of hiring the crypt for drinks and we are now introducing bespoke tours for business people. We also have a dedicated space for lectures and so on.”

The “dedicated space” is in keeping with the development.

A modern place incorporated cleverly into the old castle precincts. You go downstairs from the cafe feeling that you are entering a dungeon — until you arrive, that is, and find that yourself in a spacious business-like space on street level with a window onto the Mound.

As for winning the award, both Ms Hirons and Ms Dance agreed that it had brought far more benefits than they expected.