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 — including a modern Italian castle, a seaside house made of refrigerator panels, a floating home that was a ferry boat and a spherical house that revolves with the sun — and find out what makes them all so unique. (Source: HGTV)