Magnus the Pious (WAR History and Lore)  

Located on the Order side of the map at approximately 12k/32k. Veer off the path that leads to Black Mire Bell Tower and up the slight incline towards the camp. At the base of the cliff to your right is a bush. Behind and under this bush rests The Canonization of Magnus the Pious.

Interacting with the pile of books will grant you the unlock.

History & Lore in Ostland