Gigantic Romanian salt mines used to heal respiratory conditions.

This fantastical icy castle is built anew every winter.

A series of modernist treehouse hotel rooms grace the outskirts of an Arctic forest.

Frequent fliers welcome in this airplane hotel.

Sleep in the hay, spin the wheel and eat grain pellets to your heart's delight.

An underground city of salt.

A medieval village holds a very modern hotel.

Live out your childhood construction fantasies in this one-of-a-kind gyrating hotel.

Survival capsules find a second life as a unique hotel.

A unique opportunity to stay the night in retrofitted sections of sewer pipe.

Where beer lovers can literally immerse themselves in beer.

Macabre museum devoted to historical Viennese murders.

A museum which takes visitors to the côté obscure of Paris.

Ever hear of the Milazzo Cage?

An ambiguous ambience emanates from this centuries old leprosy quarantine.

A resort destroyed by a mysterious bombing offers visitors only its remains and the riddle behind it's demise.

A site where “the ravages of the war are more striking…than any other place in contemporary Spain.”

The vast, legendary catacombs hold secrets much stranger than stacked bones.

An Austrian house of bones filled with hundreds of intricately painted skulls.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

This small chapel is built of human bones and decorated with a golden skeleton.

Underneath this small church are 15,000 bones, arranged by an obsessive academic.

Skulls from the plague of 1656 and World War II bombings are united by a cult dedicated to caring for the ancient dead.