A Book of Knowledge is how you gain abilities for Eivor to use in Assassin’s Creed Valhalla. You can find them all over the game, and when locations in the River Raids open up, a book of knowledge is typically available alongside it. For example, in the River Erriff region, there’s a book of knowledge you can acquire if you delve deep enough into enemy territory. This guide details where to find that book of knowledge and where it is in River Erriff in Assassin’s Creed Valhalla.
The book of knowledge will be at Stag’s Eng, on the west side of the river. You want to hug the left side of the river and continue past The Farmyard. It will be the first settlement on the left side.
You want to make your directly through the village and look for a large red door that requires you and a partner to open up. Once an NPC Viking approaches to assist you, it opens up a pathway underneath the settlement. Follow the path, and you’ll be led to the book of knowledge.
Once you open the item, you’ll gain the ability called Precision Axe Throw. When used, Eivor targets an enemy’s weak point and performs a devastating attack against them.