During the Gilded Age in the late 1800s, railroad tycoon Cornelius Vanderbilt was the richest man in America with a net worth of $100 million (around $200 billion today), more money than the US Treasury had at the time.After Cornelius' death in 1937, his son William Vanderbilt took over the businesses and doubled his father's fortune. He died the wealthiest private individual in the world in 1885.William's son Frederick Vanderbilt and his wife, Louise, purchased the 153-acre Hyde Park property in 1895. Construction on the mansion began in 1895 and was finished three years later. In total, the Vanderbilts spent $660,000 to build the home (more than $23 million in today's money) and $1.5 million (around $53 million today) to furnish it.Frederick and Louise didn't have children. After Frederick's death in 1938, he left the house to Louise's niece, Margaret Van Alen. The Vanderbilts' neighbor in Hyde Park, President Franklin D. Roosevelt, then suggested preserving the estate by converting it into a national park.The Vanderbilt Mansion opened to the public in 1940.The only way to see the inside of the mansion is through a guided tour with a park ranger.Tours cost $10 per person and are offered on Thursdays, Fridays, Saturdays, Sundays, and Mondays at 10 a.m., 12 p.m., 2 p.m. and 3 p.m.The Vanderbilts' largest home, the Biltmore Estate in Asheville, North Carolina, features 35 bedrooms, 43 bathrooms, and 65 fireplaces.The Vanderbilt family also had homes in New York City, Rhode Island, and Massachusetts.The building was designed by architects McKim, Mead & White and built by Norcross Brothers. The exterior is made of Indiana limestone.The Vanderbilts used the home as a seasonal escape in the spring and fall. It has six floors and a total of 54 rooms.The oval-shaped entrance hall was furnished with green marble imported from Italy.Unlike most residences at the time, the mansion had running water and electricity.The office contained a private bathroom that led into his den.The den included a small library of books and a moose head mounted to the wall.The Vanderbilts hosted their first housewarming dinner party in May 1899, and only entertained about once per season.The carpet measures about 20 by 40 feet.Decorated with antique Renaissance furniture, the living room featured Circassian walnut panels on the walls.Frederick and Louise had a permanent residence in Paris, which inspired the Louis XIV-style decor.Vanderbilt butler Alfred Martin told the National Park Service that when the door to the salon was closed, that was a sure indication that Mrs. Vanderbilt did not want to be disturbed.The railing of the staircase was coated in velvet to make even climbing the stairs a comfortable, luxurious experience.The second floor housed Frederick and Louise's bedrooms, as well as her dressing room and several guest rooms.When I visited in January, the guest bedrooms were staged to appear the way they would have at that time of year. It took servants weeks to cover and uncover every item in the home with custom-made sheets.In European palaces, railings around royal beds were utilized during daily ceremonies when a monarch woke up or during royal births. In Louise's bedroom, the railing was merely a decorative homage to the French architecture she loved.Her room connected to Frederick's through an adjoining door. Frederick's room was closed for restoration when I visited.The basement is also where servants stored the estate's wine and spirits, did laundry, and brought food up to the ground floor through a dumbwaiter.The mansion employed 18 servants total.The mansion is situated on 153 acres of land in the scenic Hudson Valley.As our tour guide put it, It's like they get to live in a beautiful landscape painting whenever they wish.