Xanadu 2.0 (United States) - Completed in 1997 - Height: N/A

Detail: Bill Gates' private residence in Medina, Washington, boasts a high-tech, eco-friendly design and an extensive art collection.

Interesting Fact: The house is named after the fictional mansion of Charles Foster Kane in "Citizen Kane." Its assessed value was approximately $131 million, as of the last known data.