Each of the old mansions along Hudson River had a gatehouse.
Here's the gatehouse for the Ferncliff estate, once owned by the Astor family. It was designed in a Second-Empire style by architect L.A. Ehlers in 1877.
It was abandoned when I first saw it, and it seemed an ideal setting for a story of the supernatural. I sketched it using pencil and gray wash, because I felt color would have taken away more than it would have added.