Horse Sand Fort off Portsmouth, Hampshire
Horse Sand Fort is one of four "Palmerston's Follies" Sea Forts off Portsmouth Harbour. The four forts are Horse Sand, No Man's Land, St Helen's and Spitbank Fort.
The Forts were built during the 1860s to protect Portsmouth and the naval dockyards from invasion by the French and Napoleon. The forts were owned by the government until 1962, and have been in private ownership ever since.
Here's some info at www.royalnavalmuseum.org/info_sheets_solentforts.htm
Spitbank Fort is owned by one of my clients (Clarenco) and can be rented for private parties as a unique exclusive retreat for up to 15 guests. If you're on the lookout for an unusual weekend break take a look at www.clarenco.com/venues/spitbank-fort/about-spitbank-fort/ .
Modesty prevents me from mentioning the marketing agency behind the Clarenco website! (ahem... www.wisetiger.co.uk)