Back in the mid-19th century, Britain constructed three Solent forts to protect its most important naval base against attacks from Napoleon III's navy. Now, over 150 years later, they're being turned into luxury island retreats.

Located in Portsmouth Harbour, the three forts include Spitbank Fort, Horse Sand Fort, and No Man's Land Fort. Once armed with 12.5-inch muzzle-loading (RML) guns, the disarmed forts now serve a wholly different purpose.

Spitbank Fort is now a luxury hotel with eight suites. No Man's Land is still under development, but will become an even larger hotel featuring 27 bedrooms. And Horse Sands is a museum.

Spitbank includes a recreation room, spa, outdoor heated pool, a Victory Bar, and a fire pit area with a spectacular view of the Isle of Wight.

Patrons can book the facility for weddings or themed events. Or you can book the entire thing for yourself and bring 17 of your closest friends.

The entire project cost over $4 million.

[Via My Modern Met; photos: Clarenco LLP via Yatzer]