Location: Villefranche-sur-Mer, France
Price: $750 million

Named after Belgian King Leopold II, the expansive Villa Leopolda is both the largest and the most expensive French villa in the world. Overlooking the Mediterranean, it was both a military hospital during WWI and a set for Alfred Hitchcock's 1955 film, To Catch a Thief. In 2011, it was purchased by an anonymous Russian oligarch, sparking intrigue.