Story Related achievement, unmissable.
This will be the next achievement you unlock after defeating Valravyn and Sutr and entering the door leading to the Bridge to Hel. Once on the bridge, as you move forward, you'll summon Norsemen which need to be defeated (or, easier and more fun, kicked/knocked off the bridge). Once across the span, you'll enter a gatehouse, where you'll get knocked silly by an axe-wielding Norsemen.
This will trigger the second wave of fighting, but shouldn't be too troubling if you've made it this far. The only tricky combatant is the first, axe weilding one, who cannot be blocked. Dodge, dodge and keep dodging until he stops swinging, then duck in to hit him a few times. When he bellows, he's about to charge, so dodge away from this and he'll stun himself when he hits a wall. Wail away on him until the stun wears off. Rinse, repeat.
After the axe-wielder, the usual cast of Norsemen will be summoned (in the usual wave pattern). Defeat them as you normally have been doing up to this point (though, don't forget you can focus (
) to get in some free shots.
Once this wave of Norsemen are defeated, you'll come across a rune door, needing three runes to open: X
: The first is in the room where you fought the second wave of Norsemen. Look up to the second floor to see two beams crossing. Focus on these.S
: To get to the second rune, you'll need to create a staircase to get to the second floor. In the hallway of the runedoor, facing the door, a lefthand hallway will lead you to a balcony (with a lorestone on it) and a staircase down to a ship. Get on the ship and walk back towards where you fought the second wave of enemies. Look at the second wave room and focus, and this should create the stairway.
Now head back to the second wave room and head up the stairs. Go around the balcony to the other side, from here you should be able to look at the center of the room toward the boat -- some wooden beams should now be forming an S shape. Focus for the second rune.A
: From the S-rune, go forward and take the ladder to the attic. Up here you'll see som obvious beams in the A shape. Focus on it for the final rune.
(Note, before entering the rune door, you can drop down to a lower area here to get the second Lorestone. Its easy to see yet easy to miss.)
Once you open the rune door, you enter a sequence of cutscenes. Once Hel erupts from Helheim's door (authors note: Hel has really unexpected, cool aesthetic) and you get knocked off the bridge, the achievement should trigger.