A Â£26,000 grant has been promised to the council to draw up plans to improve the Lord's Garden in Ruthin.
Denbighshire council says 100 people who braved snow and ice to attend an open day at the weekend is testament to the local support for restoration.
The authority now has to learn more about the site's history and plan for its future to win the necessary cash.
Wendy Williams, of the Lord's Garden Restoration Project, said: "The bid will need to be a balancing act between staying faithful to the tremendous amount of natural and political history in the gardens, and making that history accessible to a modern audience.
"The gardens have been virtually untouched for decades, and whilst they're a beautiful wilderness, at the moment you have to be an expert to interpret the wonderful sights and sounds.
"We'd like to work with local people to try and find new and sympathetic ways of bringing that history alive again."
The Lord's Garden is now part of Nantclwyd y Dre in Ruthin, which is thought may be Wales' oldest timber-framed town house.
Although the Grade II-listed gardens, originally known as The Lord's Acre, pre-date even this structure.
They are first mentioned in 1282 as having been awarded to Marcher Lord Reginald de Grey along with Ruthin Castle, in recognition of the part he played in subduing an uprising by Llywelyn ap Gruffydd, the last native prince of an independent Wales.
The Lord's Acre appears to have remained an orchard and kitchen garden to the castle's occupants for around 350 years, and many of the fruit trees there date from between 1300 and 1600.
By the time of the English Civil War in the 1640s, the Lord's Acre passed to the Nantclwyd y Dre estate, and the focus seems to have shifted more towards meadowland and ornamental gardens.
Next month archaeologists are planning a dig at the site to try and throw more light on the role the area played in the Civil War.
But before that, the heritage service wants to give local people the opportunity to see the gardens in their untouched beauty.
"Until now we've been unable to open up the gardens, but as part of the public consultation into the proposed restoration, we're throwing open the gates for the first time," said Ms Williams.
"We'd love to hear from local historians and amateur detectives about what they've been able to unearth about the history, and we welcome any ideas about how we can make the gardens a valuable learning resource.
"But it doesn't matter if all you want to do is come along and have a look, because they really are a hidden treasure which we'd love as many people as possible to see."
Hopes of restoring a 13th Century garden in Denbighshire have been boosted by the Heritage Lottery Fund.