The Vanderbilt Mansion - Hyde Park, NY
How did we even make it to number 7 without mentioning a Vanderbilt yet? The Vanderbilt Mansion, historically known as Hyde Park, was procured by Frederick W. Vanderbilt and his wife in 1895 for use as a seasonal country home. (I tooootally have a 54-room seasonal country home too!) In 1940 the home was designated a National Historic site and by 1940 the estate was added to the National Registry of Historic Places by 1966. Today the National Parks Service maintains almost 200 acres of original land, half a dozen hiking trails, and the interiors/art of the mansion itself and adjacent buildings.
[Photo via National Parks Service]