World's Most Secret Homes.

From extravagant underground bunkers to cabins on remote islands. Homeowners discuss what attracted them to such unusual and secluded properties. A round the world tour of some spectacular homes, using drone photography to explore the natural surroundings of each home and 'fly-through' tours of their interiors and secret passages, to reveal what makes them unique. The owners explain why they wanted to live in such an unusual property, and how they found their secluded plots.