In the curious Australian outback town of Coober Pedy, much of life takes place underground in order to escape the relentless heat above.
Dubbed London's "first and only underground hotel experience," Zedwell Underground is designed with deep sleep in mind.
An eye-openingly impressive feat of engineering, InterContinental Shanghai Wonderland is one of the most ambitious hotels ever created.
A small cave hotel in Italy's famous rock-hewn town of Matera, which is a UNESCO World Heritage Site, La Dimora di Metello features just four large suites and a spa that have been excavated from the stone.
Once part of the 17th-century Marmoutier Abbey, Les Hautes Roches on the banks of the Loire River is now an exclusive 12-room hotel.
For at least 500 years silver has been extracted from the Sala Silver Mine, which once held one of the five most significant silver deposits in the world.
A sprawling salt mine in operation since the 13th century, Poland's Wieliczka Mine is a bizarre but breathtaking destination.
Located in the rustic village of Vals in the scenic Swiss Alps, this extraordinary villa is simultaneously very high altitude and underground.