You can find book of knowledge locations all of Assassin’s Creed Valhalla, adding an arsenal of abilities to Eivor’s skillset. These abilities will enhance Eivor’s capabilities in battle, giving you much more diversity in how you defeat opponents. You can find one of these books on the River Rhine, which requires you to work your way through the River Raids content of Valhalla. This guide details where you can find the book of knowledge on the River Rhine and the ability you can unlock.
You’ll need to work your way through the quest called Lugh’s Legend, where you’ll have to find all of the pieces of Lugh’s armor and then defeat the champion wielding his spear. After that, you’ll learn about the location of the River Rhine, located in Frankia, and you’ll be able to visit it whenever you’re ready to embark on those raids.
The book of knowledge is in the final settlement on the river, at the Monastery called Ferrière. When you reach the location, you’ll have to fight through the entire Monastery to make it to the top area, and then when you reach the final tower, you’ll have to climb to the top of it to reach the book of knowledge.
Inside the book, you’ll learn the ability called Spinning Harpoon. It’s a melee ability where Eivor performs a spinning attack that connects into a powerful finisher. Any enemy caught in the spinning attack will be knocked back.