In Assassin's Creed Valhalla you can come across Cairns that will give you extra points. On this page of the guide you will learn where to find locations with Cairns in Asgard.
The cairn can be found in the southern part of the region, among the mountains.
It is a very simple task. Arrange the stones so that the entire structure breaks through the blue marking. You don't need to use all stones, four will be enough. To make the task easier, we marked them in the above picture.
This will give you an extra skill point.