Separated from the city centre by the traffic of a busy main road, Cardiff Castle has long divided architectural historians and the public, many seeing it as gothic whimsy rather than a "real" castle.

The transformation of the castle in the 19th century gave the impression, superficially at least, of a medieval fortress worthy of Walt Disney. But when walking through the main gates, visitors soon learn that appearances can be deceptive.

Those willing to suspend belief and look further have always been able to discover that the present castle is the result of more than a thousand years of construction and reconstruction. But it was only with the opening of a new interpretation centre in June that the story of this Cardiff landmark has been properly told.

The new centre is close to the castle entrance and the three-floor structure is built into the battlement walls and grass banks of the fortress itself. The design is modern and utilises steel and glass to allow as much natural light into the building as possible.

As a result, the interior is light and airy and the modern feel to the structure is softened by the use of wood panelling, making the centre comfortable and welcoming to the visitors. Outside, it is no surprise that part of the roof has been planted with turf to help blend the new building into its historic surroundings.

Entering the building, signage and layout are confusing and the eye is drawn not to the cafe or information desk, but instead to a large section of Roman wall from the original 1st-century fortress that was discovered in the 1920s and which dominates the ground floor, highlighting the long history of the castle. The exhibition proper begins on the first floor and although helpful staff directed me to use either the lift or stairs, this is not obvious to visitors.

The introductory exhibition takes the form of a graphic timeline illustrating the history of the castle through the ages; it is a pity though that more objects could not have been incorporated into the displays, especially given the excavations that have taken place within the castle walls in recent years.

The introductory film is more imaginative. Much effort has clearly been spent on the 10-minute widescreen presentation, which combines animation and film, using young actors to tell the 2000-year story of the castle and the city. Once this is over, visitors are then sent down a long corridor with windows looking out from the castle on to the hustle and bustle of modern Cardiff.

Given the size of the castle and its grounds, the choice of an audio tour to tell the rest of the story is unsurprising. Not everyone is comfortable with this form of interpretation, but this one works well.

The team at Cardiff have resisted the temptation to barrage visitors with opportunities to listen to commentary at every turn. Instead they have thought hard about the location and frequency of places where the story can be heard. The result is that the perception of Cardiff Castle as a Victorian oddity is soon dispelled and the long history of the stronghold is revealed as one walks around the site.

The tour begins on the battlements, which the audio guide reveals were built less than a century ago following the discovery of the walls of the Roman fortress in the 1880s.

The new castle walls were built on the remains of the original 1st-century structure and can still be seen today. The castle walls provide a marvellous vantage point to look in at the large castle green and Norman keep and also out towards the modern city.

The audio commentary shows how successive owners of the castle have retained or destroyed the work of their predecessors. This is clearly illustrated close to the motte and bailey of the Norman castle, where in the 1770s, the efforts of Capability Brown to beautify the grounds by demolishing earlier buildings and filling in the moat were much criticised by visitors at the time.

In most cases, the tour is complemented by graphic panels giving basic information for those unwilling to use the audio guide and providing additional contemporary illustrations of the castle and its surroundings to augment the commentary.

The audio tour is confined to the castle grounds and does not extend to the interior of the castle apartments. The castle has always been the residence of some of the most powerful families in Britain, but its transformation into a "medieval dream palace" by the 3rd Marquess of Bute and the architect William Burges is a story in itself and is well-told by the old-fashioned medium of the guided tour.

The reconstruction of the castle in the 19th century dramatically changed the city skyline and although today its clock tower and faux-medieval walls, which are surrounded by 21st-century traffic, may give an impression of Victorian fantasy, there is far more to the castle than this.

The new interpretation centre and its audio tour have realigned its story, placing the 19th-century development in more context and showing its 2000-year history in a sharper focus than before.

Tim Bryan is the head of collections at the Heritage Motor Centre, Gaydon
Project data

Cost: £6m
Main funders: Heritage Lottery Fund, Visit Wales, Cardiff Council
Architect (interpretation centre): Niall Phillips Architects
Exhibition design: Laurie Stewart at Furneaux Stewart Design
AV: DJ Willrich
Audio tour: Acoustiguide
Lighting: OPCO Construction