Fear not. If you get cold during the night, there's a bar in there too.
fear not in this sentence means "don't worry" can be used to mean don't be scared etc... so if you get cold you can go to the bar, this is where they sell alcohol drinks and when you drink them it makes you feel warm or maybe they sell hot chocolate also.
Should the novelty of sleeping in a nicely appointed igloo wear off, you can always step outside and gaze up at the Aurora Borealis.
so if you get tired or bored of being in the igloo you can go outside and enjoy the Aurora Borealis.
Jason Nagata