The Arctic is where Valka had been carried off to by Cloudjumper, and where the Bewilderbeast offered sanctuary for her and the dragons she resued from Drago Bludvist's trappers and traps for 20 years.
The Arctic wastelands of the far North are full of ice, which covered much of the archipelago like an ice age. It's home to blustery arctic dragons that adapt to the most chilling conditions. It was also home to the rare mighty alpha dragon called the Bewilderbeast. It was also where Valka protected dragons with Cloudjumper. Since the attack from Drago in How to Train Your Dragon 2, the Arctic wastelands are no longer a hospitable home for any dragon, without the companionship and protection of the alpha. It is possible that the could be made habitable again, and a new alpha could start it's nest there.