This page offers a guide on where to locate and how to complete Nostalgia, which is a Mystery located in Oxenefordscire, Assassin’s Creed Valhalla.
Speak to the Elderly Farmer
This Mystery can be located southeast of Oxeneforda. The man is old and a little blind and he believes that you are his long lost child. He will first ask you to help him carry the crates to his right over to by the hay bales.
Once you’ve done that, he’ll ask you to accompany him on the benches whilst he tells you a story about his life. You’ll need to occasionally ask him to continue the story as he’ll fall asleep mid narration, but then when his story is over he’ll offer you his wife’s ring, since he thinks your his child. You can choose to take it or you can let him keep it, it’s entirely up to you. When you finish up the dialogue, the mystery will be completed.