Taal (WAR History and Lore)  

This unlock is located inside the RVR lake, so if you happen to be over-leveled for the area and are coming back to complete your unlocks, prepare to be poultry.

At approximately 7.6k/52k you can interact with some Wine in a Casket. Doing so will grant you this tome unlock:

History & Lore in Troll Country