I stumbled on this picture from A+S Error of this fantastic subway!
(See first pic) http://www.aserror.com/xe/s2down/13516
I've tried to recreate the same underground subway look with no success. When I use the constrain floor cheat to sink in the foundation or walls all is well. It isn't until I turn the cheat off to make the rest of the ground normal to cover the hidden area that the sides around the the sunken area do not rise back to it's regular floor height. I've tried looking for tutorials on this will no success, just ones on underground garages.