What the achievement asks
Unlock the Heart Forge in the repaired Chamber of Heart. Ten points.
This one is not tied to your account, so it has to be done on the character carrying the neck.
It is a step in the patch 8.2 storyline
The Heart Forge is what lets the Heart of Azeroth take Essences, and it arrives through the Chamber of Heart questline rather than through any grind.
There is nothing to farm and no drop to wait for. The chamber has to be repaired and the forge unlocked, and both happen as the story runs.
What has to be done first
- Have a Heart, the neck itself, since nothing here exists without it
- The Battle for Azeroth introduction for your faction, which is what puts you in contact with Magni at all
What it unlocks
The forge is the gate on the rest of the category. Essences cannot be slotted, upgraded or swapped without it, which means both of the remaining Heart achievements sit behind this one:
- Power Is Beautiful wants any Essence at rank 4.
- My Heart Container is Full wants rank 3 or better in every slot.
Doing this early costs an hour and removes a blocker from everything else in patch 8.2 and 8.3.