Sao, I've been there with my family. But it's been so long, I don't remember whether I was in the actual home.
My mother remembered it as a place where she'd ordered custom pottery while living nearby and teaching military dependents at the now-closed U.S. air base, Sculthorpe. This would have been in the late '50s. When I get home from work, I am going to have to check the mugs I have -- they were previously in my parents' home -- to see if there is reference to Holkham Hall on the bottom.
Funny. Though I don't remember going inside the home -- and I'm pretty sure we didn't -- I do remember there being a ferris wheel and other somewhat run-down looking carnival rides on the property.