I think I’ve found everything there is to find. I’ve visited seven rooms (Library, Tea Room, Trophy Room, Closet, Clock Chamber, Kitchen, Wine Nook) in both regular and verso mode, and I have the mirror, reflective ball, and the gold key. I’ve unlocked all of the wooden doors, either with the key or by unbolting them from the other side.
I have found that I can reverse the compass directions of both the regular and verso worlds, but I don’t really see why I’d want/need to.
I assume my objective is to escape up through the trap door in the Library, but I can’t see any way to do that.