Let me be more specific. I have a pretty good idea what the areas where "the lunatics" are kept look like, but what about the entrance? The corridors? This is a large country estate by the ocean that has been sold and converted into a private madhouse, as was occasionally the custom in those days. It is an enormous building, with two wings, three stories high, and what was once an imposing entrance in front of an entry garden (sorry, can't think of a better term). I'm guessing the inside of the house would have been extensively remodeled. I'm thinking something along the lines of the Chateau D'if, but nicer.
I've gone to Google images "inside of a madhouse", "18th century madhouse interior". On ask. com, "What does the inside of an 18th century madhouse look like?" and "18th century madhouse interior". The only thing this has netted me is Nelly Bly's "Ten Days Inside A Madhouse." All of the "crazy people" there are women, and eat in communal dining rooms. I don't want anything communal unless it was the common thing in those days.
ETA: THANK YOU! Great stuff as always!