World's Most Secret Hotels

This episode explores Bolivia's Salar de Uyuni, a striking brutalist lodge seamlessly blending in with the edge of the world's largest salt flat. It also features a futuristic getaway of bubble domes in County Fermanagh in Northern Ireland, a mirrored resort overlooking a majestic Norwegian fjord, an art deco hotel nestles amid the Pyrenees, and the extra-terrestrial-inspired design of a unique homestay in Wales.

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.

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

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 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 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.