The reason was to protect Portsmouth from an attack from Napoleon III. It has been turned into a luxury hotel, with 23 bedrooms, a lighthouse penthouse suite, spa, cabaret club, bars, restaurants and hot tubs.

InterContinental Shanghai Wonderland.  

 Built in an abandoned quarry close to Shanghai this Hotel has 2 floors under water where you can watch fish passing by. The upper floors all have amazing waterfall views. Can cost up around $500 per night to stay.

The Dog Bark Park Inn, Idaho, USA

The Dog Bark Park Inn takes the term ‘dog lover’ to a whole new level. Owned by chainsaw artists, the B&B is located inside a 12-foot beagle. Guests (it sleeps four) enter the beagle’s body through the 

second-story deck. It is, of course, pet-friendly.

Hotel Marqués De Riscal, La Rioja, Spain

The Marqués de Riscal is architect Frank Gehry's first and only hotel project, located in Elciego, in the heart of Spain’s Rioja wine-growing region. Similarly to his other projects, such as the Guggenheim in Bilbao and the Foundation Louis Vuitton in Paris, the structure is avant-garde in its approach, using huge titanium ribbons which stand out from the surrounding vineyard. 

Inntel Amsterdam Zaandamn, Amsterdam, Netherlands

The façade of this hotel is made up of nearly 70 stacked houses – from labourers’ cottages to town houses – which are typical of Amsterdam. Rooms are inspired by local history and there’s also a spa with a pool, Turkish steam bath and Finnish sauna.

Skylodge Adventure Suites – Peru

This is the ultimate high-rise experience: sleeping like you are in a condor's nest. A group of transparent, luxurious capsules hangs from the top of a mountain in the Sacred Valley of Peru.

To sleep at Skylodge, guests must climb 1,300 feet of Via Ferrata or hike 40 minutes to the first zipline. Each capsule suite houses four beds, a dining room, solar-powered lighting, and a bathroom.

De Bossche Kraan

's-Hertogenbosch, North Brabant, Netherlands

An architect-designed ‘luxury hotel room' in a crane nestled above the water, with rotational Old Town and city views from the south of the Netherlands.