_Spitbank Fort: Explore the floating 8-bedroom home off the coast of Portsmouth

Guide price: £3,600,000

A unique investment opportunity for a buyer with strong sea legs, a keen sense of adventure and a strong desire for total privacy, nothing about the 19th century Spitbank Fort is conventional, but therein lies its inimitable, James Bond-style charm. There isn't anything quite like it floating anywhere in the world.

Rising off the coast of Portsmouth and the Isle of Wight at the mouth of The Solent, hugged by transitioning seascapes and accessed only by boat, Spitbank Fort stands in the middle of the approach into Portsmouth Harbour flanked either side and to the front by its two sister forts: No Man’s Land Fort and Horsesands Fort.

Sympathetically restored with many original features, Spitbank Fort is currently operating as a floating, 9-suite luxury retreat with sauna and spa. The officer's mess provides a 60-cover restaurant.

A sure conversation starter at your next dinner party, the circular sitting room forms the principal entertaining room and has a bar and three ante rooms; one of which has retained the original wash basins from Napoleonic times.

Accessed off the central courtyard is a corridor that provides access to the 8 luxury, en suite bedrooms. Each themed bedroom has its own sea view, as do both receptions rooms.

All the rooms have retained many original features including the metal tracking for the cannons and iron hooks for the hammocks. Also on this floor is the office, library and additional bathrooms.

External steps lead up from the courtyard to the upper deck that is dominated by the Crow’s Nest self-contained annex that is ideal as entertainment space. It enjoys panoramic views of the Solent and has a shower room, toilet and a bar. If required, it can be used as the 9th bedroom suite (excluding staff accommodation). Also on the upper deck are the sun decks, a fire pit, hot pool and sauna.

External steps lead down from the courtyard to the lower deck where staff quarters are located. Completing the living space is a games rooms, a wine cellar, bar and television room as well as many other storage rooms and services rooms to provide power, water and sewage facilities.

The history of the forts is storied and dates back over 150 years; originally commissioned by Lord Palmerston - nicknamed the 'Palmerston Follies' - as British sea defences to defend Portsmouth against a less-than-imminent seaborn attack by the French.

Never used for their original purpose, the forts later housed soldiers in both the First and Second World Wars before being decommissioned and neglected until the 1960s.