This page of our AC Valhalla contain walkthrough for all World Events appearing in Eitri region.
Location: Eastern part of the city, right next to the border with Svaladal.
Start by talking to the man marked by the quest marker. Follow him all the way to the building. Do not overtake or rush him. Along the way, you'll listen to his story.
Once you reach the area in question, pick up a toy hammer from the rubble and talk to the man. There is a choice before you, but it doesn't really matter which option you choose. After the conversation, the mission will end.