Way to unlock: Automatically after retrieving the first Keystone
The quest-giver: - (M22,3)
Quest can be activated doing other one, named: "A Tevinter Relic Hunt". The opportunity will appear after reaching the Still Ruins located in the central part of The Western Approach. Head to the northern part of the ruins (M22,3) and defeat the Lucanus. After the fight, search his corpses for the Keystone.
The game will show the location of the other four keystones (M22,3a), so that you will have to begin the searching right away. You shouldn't have any problems with finding these items, they are not guarded by anyone either. Having all keys, head to the closed door (M22,3b) and use them to enter the sealed chamber.
Rewards for completing the quest:
- Experience (mediocre amount)
- 80 Influence Points