In Assassin's Creed Valhalla you can come across Cairns that will give you extra points. This page of our guide has the Cairns locations in the East Anglia region.
You will find the cairn in the northern part of the region, right next to the river.
It is a very simple task. Arrange the stones so that the entire structure breaks through the blue marking. On the screenshot above we showed the most optimal construction, nothing should happen to it.
This will give you an extra skill point.