Enter Permafrost, head to the back room (circular and may have Vision of Vox in it, you can skirt around her without aggro), go to the right and upward. You need to keep going up until you reach level 3. It's at the top of the castle, so when in doubt, go upward.
Note: You no longer need the access quest unless you're interested in the lore.
There is a time lapse between mobs becoming aggro, sort of like a ring event. The golems go aggro, then the wolves, then the King. The King spawns two sets of giant adds which seem to make him go immune to damage, then a set of skeletons which don't seem to make him immune. Put your back to a wall to avoid being kicked across the room away from the healer. Not much trouble at level 55 with a mercenary but still a challenge.