Bingowings said:
an inexplicably placed hole in the floor
You bring this up all the time. It's there because it looks impressive (Both within the film's logic and from a moviegoing perspective). This is a real-life building in China...
^ That inside space could have been used to fit in more offices (Or cellblocks and garbage-mashers) but for some reason they left it empty? Maybe the architect designed it in the hope that somebody would use it for the same purpose that Vader did ;-)