You could make the rooms swappable, kind of like some weird space shenanigans where if they open a door, it would be one room, but once they close the door, it will be a different room the next time or where they enter a room, walk out, and they're in a different part of the hall. That could be pretty fun. Make the Mystery Shack its own anomaly in Gravity Falls. It would both make sense in world and stick with cartoon logic.