The Bone Witch in Njorndar Village wants you to defeat Iskalder upon Battlescar Spire.
Atop the tallest peak to the southwest overlooking Jotunheim is Battlescar Spire. It is a place of reverence for the vrykul, second only to Valhalas in terms of where they prefer to do honorable combat.
We shall visit not-so-honorable combat upon it.
Gather your companions and fly to the spire. When you are ready, light the signal fire and I will appear within the body of Iskalder.
We will fight, you will win, and Vardmadra is sure to come to witness the battle!