Finish the Masterwork Weapon is an early game quest that you can pick up while wandering the Blighted Village and reading Highcliff's journal in Baldur's Gate 3. The quest concludes with finding the Melting Furnace to obtain a Sussur Weapon.
Where to Find Sussur Bark for Finish Masterwork Weapon Quest in Baldur's Gate 3
In this guide you will learn exactly how to get to the Forge in BG3 so that you can complete the quest 'Finish the Masterwork Weapon'.
The Melting Furnace is located in the Blighted Village behind some Shabby Doors, or more specifically, at (X: 46, Y: 412). The Melting Furnace is the final piece of the Finish the Masterwork Weapon quest. With the Sussar Tree Bark in your inventory, along with a standard Greatsword, Dagger, or Sickle, you can use the Melting Furnace to craft your Sussur weapon.
However, don't go up the stairs and into the main part of the house. Instead, you need to break down the basement doors, right below where a goblin guard is standing (or was, if you killed him). Once the door is unlocked, go inside and go down the stairs until you see a fireplace.