Aha! The latest preview clip has answered my curious inquiries.
It also shows that they're exploring the new console room set. Looks like the lower floor is still used for storage in general, though in this case it has part of the current Doctor's wardrobe. Where does he keep the bike we see him and Clara ride later on?
Looks like the two staircases leading down from the console room floor lead to a landing and then split into two further staircases leading to the bottom floor (a little redundant IMO). A little strange that you can have one way up to get to two exits, four ways to get down to the closet. and apparently only one exit. :P
Also in stark contrast to the rest of the set (and every console room since 1996), the storage locker seems to be made at least partly of wood!