Baconsthorpe Castle has been closed to visitors for urgent works, but its custodians are keeping tight-lipped about what is being done or how long it will take.
The 15th Century ruined, moated manor house east of Holt has been put off limits by English Heritage following an initial survey of the site.
But a spokesman for the charity was unable to say how long the attraction - which draws visitors throughout the year - will be closed.
The spokesman said: "The remains of the castle, which are in the care of English Heritage, are particularly vulnerable and the charity is currently in the process of surveying the site with a range of specialists and experts to provide a more detailed understanding of the conservation work now necessary to care for and protect the site for the future.
"In order to enable visitors to continue safe access to the inner bailey, work is underway on the castle’s gatehouse. With this being the only entrance to Baconsthorpe, the inner site is temporarily closed while these works take place."
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