The word extreme means different things to different people, and to these homeowners it means pushing the envelope as far as possible. From construction to completion, take an up-close look at some of the world's most spectacular houses ever built - from a home carved right into the side of a red rock canyon to one that is built completely underground, from a home suspended in mid-air to one that is concrete from the floors to the furniture - and find out what makes them all so unique.