Here are some great links to the history of the Senator William Clark mansion which was located on 77th Street and Fifth Avenue. It was at the time of construction considered to be the grandest and most ostentatious mansion in New York City. It was this house that mysterious heiress Huguette Clark lived as a child.
Wikipedia about house
Wikipedia about Senator Clark
The Salon Dore
New York Times story on the death of Huguette Clark