Rick Mather Architects has submitted a planning and listed building application for a £4.46m restoration of Hay Castle. When the project - which will benefit from grant funding from the Heritage Lottery Fund - is complete, the castle will be open to the public for the first time in its 800-year history.

The Hay Castle Trust, Rick Mather Architects and the project team has required a close working relationship with Brecon Beacons National Park Authority, Powys County Council, Cadw and The Royal Commission on the Ancient and Historical Monuments of Wales to create a scheme which preserves the historic building and breathes new life into the Castle for future generations. The scheme will restore and conserve the critically at-risk medieval keep and the mansion; restore and open the ancient gate - the oldest of its kind in the UK; reinstate the vital connection between the castle and the town; and create a culturally and economically vibrant centre for the arts and training.

A museum-standard gallery will host touring exhibitions from major collections, a platform high in the castle keep will create a memorable visitor experience of this ancient monument, and a characterful learning space will engage young and old. The project will create new jobs and support the regional economy. Hay Castle will be a major heritage destination, with free access for everyone.

Nancy Lavin Albert, managing director of Hay Castle, said: "We are grateful to the Heritage Lottery Fund which does crucial work saving irreplaceable buildings across the UK. We are extremely grateful to all our supporters for their generous donations to this ambitious project. The Trust's aspiration is to create an inspiring place for people to enjoy their heritage and the arts, learn new skills and participate in cultural and community events."

Head of the Heritage Lottery Fund in Wales, Richard Bellamy, said: "While an incredibly ambitious piece of work, there is so much more to this than simply restoring and preserving a significant piece of Welsh history - it's also about ensuring Hay Castle continues to be a meaningful place for people today." In addition to the award of £4.46m by the Heritage Lottery Fund, the Trust has also raised over £1m with the help of its supporters. However, £900,000 still needs to be raised by the end of this year in order for work to begin on site in 2017.

Elizabeth Haycox, chair of the Hay Castle Trust, said: "Hay Castle is currently in a critical state of disrepair so this announcement today is great news for the town, both culturally and economically. In addition to seasonal tourism attractions, the Trust is developing a year round programme of activities focusing on literature and Hay's unique position as a book town."