This achievement is unlocked when you complete the main quest, “
The Coming Storm.” It is story related and
cannot be missed. The quest is available when you complete the two pre-requisite main quests, “
Old Friends, New Foes” and “
The Hunters Hunted.” Completing both these quests triggers “The Coming Storm.”
Go to the
Gardens of Ysa. Enter the doorway to
The Font. Follow the path and enter
The Court of Summer. Place the codex on the pedestal as indicated by the amber arrow quest marker. Following the ensuing dialog with High King Titarion, you will receive your quest reward and unlock the achievement. as shown in the following twenty second video: