This is quest related, to access the area where the quest giver is located you will need Stoker’s Boots which allow you to safely walk in fire biomes.
Stokers Boots are crafted at the Blastforge with 3 Scrap Iron (from exploded mines or robotic enemies), 1 Piston (best acquired from Supervisor robots), and 2 Freezing Slime (you must throw a Flash Bomb at a Smoke Ghost and use the Milker on it while it’s stunned).
To unlock the Blastforge please see the
achievement.
The area is Lost Industry which will be in the easternmost area of the game (just below the Heretic’s Cavern, aka the green area with Verdite in it. The quest giver is right by the Travel Tube in the Lost Forge, the quest giver will give you three quests, the final quest is to bring an item from The Craftmaster and show it to the quest giver, after which a short story event will occur and the achievement should pop.
If you have a Telescopic Key there is a large chest a few steps west of the Travel Tube that contains the Powder Keg bombs that you need for the middle quest step. If not you can craft them at the Blastforge with 1 Anglermole Lantern (from the hopping monsters in snowy areas, you need a hammer or bombs to engage them), 2 Brimstone (smash the mounds in fire biomes with a hammer), and 3 Ash (found most easily from Stoker kills, but often on the ground in industrial biomes). See the
achievement for details.