We uncover some truly remarkable and hidden retreats in Canada, Iceland, Sweden and the UK - from underwater sunken hotels to remote retreats surrounded by lava fields.

We uncover some truly remarkable and hidden retreats in Canada, Iceland, Sweden and the UK - from underwater sunken hotels to remote retreats surrounded by lava fields.

We travel to the Scottish wilderness in search of spaceships, the Welsh mountains to probe mysterious spheres, a Greek tower with a deadly history, and an Italian hotel perched on a glacier.

We travel to the Scottish wilderness in search of spaceships, the Welsh mountains to probe mysterious spheres, a Greek tower with a deadly history, and an Italian hotel perched on a glacier.

More hidden hotels are revealed in Uruguay, Sweden, Scotland, Oman and The Netherlands - from a camouflaged resort perched on the edge of a mountain, to mainland Britain's most isolated hotel.

More hidden hotels are revealed in Uruguay, Sweden, Scotland, Oman and The Netherlands - from a camouflaged resort perched on the edge of a mountain, to mainland Britain's most isolated hotel.

We visit the TWA Hotel, hidden within one of New York's busiest airport runways, and Kakslauttanen Arctic Resort's glass igloos in Finnish Lapland.

We visit the TWA Hotel, hidden within one of New York's busiest airport runways, and Kakslauttanen Arctic Resort's glass igloos in Finnish Lapland.

We uncover more unique and unusual hotels in Jordan, England, Sweden and Ecuador, including the Bubble Wadi Rum Luxotel resort that resembles a colony on Mars and a converted plane.

We uncover more unique and unusual hotels in Jordan, England, Sweden and Ecuador, including the Bubble Wadi Rum Luxotel resort that resembles a colony on Mars and a converted plane.

In Cambodia we visit the Shinta Mani Wild hotel on the banks of the Timor Rung River, and in Italy, a clifftop settlement that's hewn into the limestone rocks.

In Cambodia we visit the Shinta Mani Wild hotel on the banks of the Timor Rung River, and in Italy, a clifftop settlement that's hewn into the limestone rocks.