Awarded upon completion of the Hordafylke arc.
This arc is avaiable towards the latter end of the game, and is started the same way as the other regions; by pleding to the area at the alliance map. It's at the bottom right of the main England map.
It's all fairly straight-forward, but there are some hints below in the spoiler tag.
*** Spoiler - click to reveal ***During the Odin fight when the door appears (after he's killed you once) just go into your equipment and unequip your axe. Then you can run through the door onwards with the mission.
During the first part Basim fight let him perform his air attack on you a few times, he'll give a bit of dialogue to move the fight on. I found that fighting back and hitting him wasn't giving me any results
If this is not available then chances are you are yet to speak to Sigurd. He's in the room joint onto the map room, go in and speak to him and he'll talk about going back to Norway