Hearst Castle, California

Hearst Castle, built by architect Julia Morgan between 1919 and 1947, was the largest private home in the U.S. during its construction, with a 90,080-square-foot main house featuring 38 bedrooms and 41 bathrooms. Its European art and antiquities collection is valued at over $300 million, and the estate's Neptune Pool holds 345,000 gallons of heated water. Annual operating expenses exceed $4 million.