It marks the 20th anniversary since the start of the campaign to preserve Gwrych Castle, near Abergele.
It was 1997 when 12-year-old Mark Baker began his campaign to safeguard the building's future.
Since then he and volunteers have saved sections and signed a lease to look after a large part of the grounds.
Gwrych Castle was built between 1812 and 1822 by Lloyd Hesketh Bamford-Hesketh as a memorial to his mother's ancestors, the Lloyds of Gwrych.
By 1989 it was sold to an American and although there were plans for its future, it began to fall into decline.
Travellers moved onto the site for two years before finally being forced to leave in 1997.
Mark Baker, now Dr Baker, an architectural historian, said he felt compelled to try to save it after walking by it daily on his way to school.
His campaign to set up Gwrych Castle Preservation Trust attracted the attention of the local newspapers and won support of community leaders.
Today, the registered charity has a 25-year lease for five acres (two hectares) of the site.
This has enabled it to begin restoration of the first section of the castle, the Countess's Writing Room in the Gardener's Tower.
Although the formal gardens are regularly opened, from this month visitors can explore the grounds themselves for the first time.
Dr Baker said public access had always been his "main aim".
To celebrate the trust's 20th anniversary, other events are also being held, including a Medieval festival on 19-20 August.
A Conwy county castle being restored by a community group after years of neglect is opening its doors daily to the public throughout August.