Hint 1
Hint 2
Hint 3
Hint 4
Getting there is easy, once Dagny tells you the cabin exists (which she does after you fix her heater) --
How do I fix Dagny's heater?
-- get the snowmobile running --
How and when do I use the snowmobile?
-- and get the key to the cabin, which Dagny told you was in Elisabet's purse.
How do I distract Elisabet?
Once you've done all that, get on the snowmobile and go. It stops at a signpost; turn left to go the cabin, forward to go to the ice caves, and back to return to Skipbrot.