Hillwood Estate.Talia Lakritz/Business InsiderHillwood Estate was the home of breakfast-cereal heiress Marjorie Merriweather Post.She collected art from 18th-century France and imperial Russia for display in her 36-room mansion.Hillwood was her fall and spring home. She also built Mar-a-Lago and lived there during the winter.Marjorie Merriweather Post was once known as America's richest woman, with an estimated net worth of $250 million, or around $1.8 billion today when adjusted for inflation.She inherited her father's Post cereal fortune in 1914, but Post helped build the company into the General Foods Corporation by acquiring brands like Jell-O and Maxwell House.