Gryttirsand is an area within the Rygjafylke portion of the map in Assassin’s Creed Valhalla.
It’s located just southwest of Notfall and southeast of Marauder’s Den.
Here’s how you can get the book of knowledge in Gryttirsand in AC Valhalla.
Location of book of knowledge – Gryttirsand
The exact location of the book of knowledge in Gryttirsand is shown in the map below, marked by the book symbol.
How to get into the room
The book of knowledge is behind a door that’s barred. To get inside the room, you need to access the tower in the enemy base.
Climb up the tower and on the first floor, you’ll see some weak planks. You can destroy the planks to open a path.
Jump down the hole and you’ll reach the room.
Grab the book and you’ll unlock the ability named Thorn of Slumber.