Exiting the viewing room, go to the top of the stairs on the right, go down the stairs, at the level make a left and down the rest of the stairs, at the bottom level stop.
Exit the room, turn left and walk down the stairs. Wait by the statues.
Face the iron railing and walk right until you get to some stairs. Go down the stairs all the way to the bottom and stop just before passing between the two white marble statues.