On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough of the Asgard side quest: Hel's Well.
Reward for completing the mission: 1200 XP.
You will find a sealed well in the location marked in the image above. There will also be a man named Motull who wants to go to Helheim to return to his wife, Ronnow. Their village was destroyed - the man died fighting, but his wife did not.
After a brief chat, you will have to decide what will happen to the soul of this warrior.
- If you fight him and, win the duel and Motull submits to your will;
- You'll tell him that he won't find anything in Helheim and explain how he should proceed. The man will obey and remain in Asgard.