4The One – Bel-Air, California, USA

Estimated Price: $500 Million. The One is a 100,000-square-foot mega-mansion located in the affluent Bel-Air neighborhood of Los Angeles.

Designed by architect Paul McClean, this home took nearly a decade to complete and includes 21 bedrooms, 42 bathrooms, a 50-seat movie theater, a bowling alley, a nightclub, and multiple swimming pools. Despite recent legal issues surrounding its sale, The One remains one of the most extravagant properties in the U.S.