I'm getting really frustrated on how we get access to the arcanum dorm rooms. I've seen people have them but they won't or can't tell me how to get them because someone got it for them. How do we get to the dorm rooms in the arcanum?! I've tried looking it up with nothing showing up. HELP!!!!!
At a certain point, late, in the storyline of Mirage quests, you will be sent back to the Arcanum. There you will be given a quest to fight a Void Elemental. Successful completion of that fight and the subsequent talking to the proper person will earn you the title Arcanum Understudy and gain you your very own Arcanum apartment.
Note: Finishing that quest also unlocks your new spell quest. :)