Go upstairs in the cabin and turn right immediately.

You should see a couch pushed against a balcony.

Look over the balcony, and you should see a mounted moose head.

Stand on the banister and hop onto the moose.

You can then move on an invisible wall.

You can keep moving further until you come to a corner.

When at the corner hop to the other side and you're on a new wall.

Great for sniping! You can also look out small windows.