Three manmade island forts off the tear of Portsmouth were placed on the marketplace for £9m.
They were constructed about 150 years in the past as share of sea defences against a feared French invasion.
Two of them, No Man’s Citadel and Spitbank Citadel, were transformed into luxurious accommodations. The third, Horse Sand Citadel, is described as a “living museum”.
The BBC’s John Maguire took a gape round.