Built in 1986 as a film set for Dream of the Red Mansion, the Rong Mansion is now used for a variety of film and photography purposes, as well as being open to the public to explore.
While I have never watched Dream of the Red Mansion nor even heard of it before, it was none the less interesting to wander around and admire the artwork and furniture commissioned from famous artists specifically for the filming. I also enjoyed exploring the many courtyards and small rooms around the building – an interesting display of what a traditional Chinese mansion may have looked like.
Unless you're a Dream of the Red Mansions fan, this is unlikely to be top of your list to see in Zhengding. However, for a quiet exploration if you have some spare time it's not a bad place to wander around.