Work to renovate and maintain a historic fort once owned by Tudor royalty and now owned by a council will take 30 years.
This revelation comes following a free public open day at Westenhanger Castle, near Hythe, which was attended by 400 interested visitors.
Guests were able to explore the ancient site, which is fitted with suits of armour and grand fireplaces, and its grounds, which were previously used for hunting by King Henry VII.
The day was hosted by new owners Folkestone and Hythe District Council (FHDC), who purchased the castle in the summer for £2.9m, plus further costs for legal bills and tax, in a bid to make it the centrepiece attraction for proposed garden town Otterpool Park.
The purchase by the authority was made possible following a decision in November 2018 from the cabinet to “purchase property to facilitate the development of Otterpool Park as necessary”.
The 10,000 home development, which will also include new schools and green open spaces, has yet to be given planning permission, although a £100m loan to kickstart it has been given the go ahead.
FHDC previously stated their plans for the castle - now used as a wedding venue - such as flooding the currently dry moat, restoring the barns and creating a public park in the 14 acres of surrounding land.
But now it has revealed that this work could take three decades in total - the same estimated length of time to create Otterpool.
A FHDC spokesman said: "The open day recently held at Westenhanger Castle was a great success.
"Hundreds of people attended, with many residents taking the opportunity to visit this fantastic community asset for the very first time and showing their overwhelming support.
"People had a genuine interest in the history of the castle and its grounds, while also asking questions about its bright future.
"We received incredibly positive feedback.
"We are currently working on a 30-year plan which focuses on its maintenance in the short term, and longer term restoration work on the buildings and grounds.
"Further open days will be held in the future."
The purchase of the castle was previously described as a 'slap in the face for residents' by opposition councillors at FHDC who suggested the money could have been spent better elsewhere.