Way to unlock: Talk to Varrik in Skyhold after completing the "Here Lies the Abyss" main quest.
The quest-giver: Varrik (M12,20)
You will recognize that the quest is available by an unknown female drawn standing next to Varrik in Skyhold. When you join the conversation, you will be given a quest. You must go to Valmmar (M3, 18a) in Hinterlands (if you don't have access to that location yet, you must take the key from the balcony in villa on west (M3,18). When entering Valmmar you will have to again choose your party members and Varrik is a mandatory companion during this quest.
There is not much work for you in Valmmar. Go to the lower level, where you can find door unavailable before near the stairs. Bianca will open them.
A few dwarves reside inside, you must defeat them. Go to the end of the room and take key lying on the table. No all you must do is return to Skyhold and talk to Varrik (M12,20).
Rewards for completing the quest:
- Experience (lots)
- 400 influence points
- 3 power points