The owners of the world's most luxurious houses can be a mysterious bunch. We all know who owns Buckingham Palace, but does anyone recognize the name Tim Blixseth? Or know the Indian billionaire who built a 27-story apartment building just for himself? We're guessing not.
Well, the mystery ends here. Using information provided by CompareCamp.com, we've got a rundown of the world's 10 most expensive houses—modern castles, really—and the people lucky enough, and rich enough, to own them.
Read next: The 10 Richest People of All Time
7 Upper Phillimore Gardens
Value: $128 million
Details: This 10-bedroom prep school turned mansion has an underground swimming pool, a sauna, gym, cinema, and even a panic room. That's all in addition to an interior covered in marble, gold, and priceless artworks.
Owner: Olena Pinchuk—daughter of Leonid Kuchma, Ukraine's second president. She is known for being the founder of the ANTIAIDS Foundation and a friend of Elton John.
Kensington Palace Gardens
Value: $140 million
Details: Located on London's Billionaires Row, the already tricked-out pad will soon add an underground extension with a tennis court, health center, and auto museum.
Owner: Roman Abramovich—a Russian billionaire and owner of the private investment firm Millhouse LLC. He's probably best known in the West as the owner of the English Premier League's Chelsea Football Club.
Seven The Pinnacle
Location: Big Sky, Montana
Value: $155 million
Details: The largest property in the Yellowstone Club, a private ski and golf community for the mega-rich, the house has heated floors, multiple pools, a gym, a wine cellar, and even its own ski lift.
Owners: Edra and Tim Blixseth—Real estate developer and timber baron Tim Blixseth cofounded the Yellowstone Club, but the club's bankruptcy, a divorce, and other troubles have seriously reduced his wealth in recent years.
Location: San Simeon, California
Value: $191 million
Details: The 27-bedroom castle, used in the movie The Godfather, has hosted John and Jackie Kennedy, Clark Gable, Winston Churchill, and other famous figures.
Owners: William Randolph Hearst's trustees—The castle, built by the country's first newspaper magnate, is now a heritage and tourist site and part of the California Park System.
Location: Woodside, California
Value: $200 million
Details: Less a house than a compound, this 23-acre property is home to 10 buildings, a man-man lake, koi pond, tea house, and bath house.
Owner: Larry Ellison—Co-founder of Oracle and the third-richest man in the world in 2013, according to Forbes.
18-19 Kensington Palace Gardens
Value: $222 million
Details: Another property on Billionaires Row, 18-19 sits alongside the home of Prince William and Kate Middleton. This particular residence has 12 bedrooms, Turkish baths, an indoor pool, and parking for 20 cars.
Owner: Lakshmi Mittal—The head of Arcelor Mittal, the world's largest steel manufacturer, and, according to Forbes, one of the 100 richest men in India.
Four Fairfield Pond
Location: Sagaponack, New York
Value: $248.5 million
Details: This 29-bedroom home sits on 63 acres and has its own power plant. Inside, there are 39 bathrooms, a basketball court, bowling alley, squash courts, tennis courts, three swimming pools, and a 91-foot long dining room.
Owner: Ira Rennert—Owner the Renco Group, a holding company with investments in auto manufacturing and smelting. He also has holdings in metals and mining.
Location: Cote D'Azure, France
Value: $750 million
Details: This 50-acre estate includes "a commercial sized green house, a swimming pool and pool house, an outdoor kitchen, helipad, and a guest house larger than the mansions of most millionaires," according to Variety. The house was famously used as a set in the 1955 Hitchcock classic To Catch a Thief.
Owner: Lily Safra—A Brazilian philanthropist and widow of Lebanese banker William Safra. Her husband died when another one of the couple's homes burned down, apparently due to arson.
Location: Mumbai, India
Value: $1 billion
Details: The Antilia isn't even really a home in the traditional sense. This 27-story, 400,000-square-foot building has six underground parking floors, three helicopter pads, and requires a 600-person staff just to maintain it.
Owner: Mukesh Ambani—India's richest man, with a net worth of $23.6 billion, according to Forbes. Ambani made his money running Reliance Industries, an energy and materials company.
Value: $1.55 billion
Details: Technically still a house, but certainly not for sale, the Queen's residence was valued at roughly $1.5 billion by the Nationwide Building Society in 2012. The property holds 775 rooms, including 19 state rooms, 52 bedrooms, 188 staff rooms, 92 offices, and 78 bathrooms.
Owner: The British Sovereign—Currently Queen Elizabeth II, who has ruled since February 6, 1952.