On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough description of the Well-Traveled mission.
A man who calls himself the Builder promises to provide Asgard with protection from enemies in exchange for water from the Well of Urdr.
Reward: 3400 XP.
Reach the Well of Urdr
Head to the entrance of the Well of Urdr, then go underground. To get to the rest of this location, aim the beam of light so that it hits the second device and opens a passage. Go further into the cave.
In the spacious grotto, you'll run into Tyr, who speaks about the Builder's request with concern. The Well of Urd is well sealed and you will have to solve a logic puzzle to get to it.
Unseal the Well
If you want, you can try unsealing the Well of Urdr yourself. However, if you need a little assistance, we've put together a detailed description of this puzzle along with an instructional video showing you how to complete it.
When the Well of Urdr is opened, jump down to the very bottom and draw some water to activate the cinematic interlude. After talking to Tyr, jump into the water, dive in, and leave the cave.
When you resurface, talk to Loki. The god of deception is very interested in the state of the water in the Well of Urd and is behaving suspiciously, to say the least. After the conversation, the mission will end and you will receive 3 400 XP as a reward.