Access via The Shadowforged City (right side through The Hall of Crafting or Ring of Law.
Clear the room before engaging the elite guarding The Vault (sometimes has a dog as add).
You need 12 Coffer Relic Keys to open all the coffers in The Vault (as a group). Do not open all 12 coffers at once. Instead open 11, then leave the room and let the tank open the last coffer.
As soon as the last coffer has been opened the golems within the room will come to life. Let the tank get aggro and focus on them one-by-one.
After the last golem fell, you can obtain the item needed for the quest The Heart of the Mountain.
The last coffer in the room can only be opened with a special key. You can obtain this key by looking at the picture of the Dark Keeper. You will get a clue to where the Dark Keeper holding the key just spawned. Travel to him, kill him and return to The Vault to open the last coffer. The loot is worth this in most cases.