Carnegie Mansion, ca. 1905.

In 1898 Andrew Carnegie began purchasing lots that would result in his owning two full blockfronts on Fifth Avenue between 90th and 92nd Streets. His choice of this land so far uptown—and away from his society peers—was purposeful. Commissioning the firm of Babb, Cook & Willard, he had built a massive 64-room mansion in the style of a English Georgian country house. The property included 30,000 square feet of outdoor space. The house, constructed between 1899 and 1902, features a number of engineering and technological innovations. It was first private residence in the United States to have a structural steel frame and the first in the city to have a residential Otis passenger elevator. The huge house was warmed with central heating. Alas, most were not impressed, The New York Tribune noted that "many people are disappointed by the plainness of the house." (Actually, that is exactly what Carnegie wanted.)

The house was occupied by Carnegie's wife until her death in 1946 (Carnegie had died in 1919). The surrounding neighborhood became known as Carnegie Hill. The home remained in the holdings of the Carnegie Corporation and served as Columbia University School of Social Work for a few decades in the mid century. Since 1976, when the Corporation donated it to the Smithsonian who opened the Smithsonian Institution’s Cooper-Hewitt Museum. After an extensive renovation that had the museum closed between 2011 to 2014, it was reopened as the Cooper Hewitt, Smithsonian Design Museum.