Ok so I might be the only one who gets this I do not know. The group is in the middle of a lucid dream which is why they are in the black going in either direction towards the white will either wake them up or they would no longer be lucid. This is where they work.
Dom Cobb and Ellen are the only two that knows what could happen if Dom knew the layout of the dream that Ellen built so they are seperated somewhat from the rest of the "dream team".
Ahh dream team I can't believe I said that >.< Anyway think this will be my last one.