It turns out that Ariadne constructed a snowy military fortress because… well, who knows. Maybe she wanted to make it as difficult and visually appealing as possible.
At any rate, there's a lot of action:
Yusuf is driving the van but gets trapped on the bridge so he has to kick early in order to get back to reality.
Arthur is evading baddies in a hotel devoid of gravity while trying to figure out how to kick everyone now that the absence of gravity has ruined the first plan. He ties everyone up and pushes them toward the elevator. We're not sure what he has planned—but we hope it works.
Saito and Robert make their way toward the safe while Eames distracts everyone and Cobb shoots people. Unfortunately, just when Robert makes it into the safe room Mal shows up and shoots him. Cobb has a chance to take her down but hesitates and only shoots her after the fact. Robert is dead and it looks like they've failed.