Balfour Castle on the Orkney isle of Shipinsay is being offered through Savills Edinburgh
Captain Tadeusz Zawadzki bought the 770-acre estate, described as the 'the most northerly castle in the world', in 1961.
It was built in 1847 by architect David Bryce, the leading exponent of the Scottish baronial style who also designed Tony Blair's old Edinburgh school, Fettes College.
Capt Zawadzki moved his Scottish wife and their four children into the castle, said to be a rare example of a 'calendar house'.
It was planned to contain seven turrets for the days of the week, 12 exterior doors for the months, 52 rooms for the weeks, and 365 panes of glass for the days of the year.
He ran it as a country house hotel until his death, after which his widow Catherine and their two daughters continued the enterprise.
His son, Richard Zawadzki, manages the rest of the estate, which includes the five bedroom Balfour Mains farm, three cottages, farm buildings, and more than 600 acres of farmland.
The islands of Muckle Green Holm and Helliar Holm are also available, while the hotel comes complete with a successful rough shoot business.
The estate is so large that it is for sale as a whole or in separate lots.
Mr Zawadzki said: 'We are selling because we're getting to the time of life when it's a bit too much to manage.'