The Caverns Beneath Derceto

Work your way from the bottom of this maze of wooden bridges toward the top, where a chest and the way forward are waiting. Skull and sword markers scattered through the maze hint at the correct path — trust them over guessing, and use Jump where a gap calls for it.

Use the Pirates' Key on the chest for the Large Gem and a book. Push aside the rock on the same ledge to continue into a pitch-black maze. Save before going in.

There's no map here, and the Oil Lamp's fuel is limited, so move with purpose rather than wandering. From the entrance: go as far left as the maze allows, then as far down as it allows, then as far right as it allows. That sequence leads to a gray stone door with a fist-sized hole in it — sized for the Large Gem you're carrying. Put the lamp out once you're at the door.

The chamber starts collapsing once Pregzt falls — falling rocks damage anyone who lingers, though there's no hard time limit forcing your hand. To the right of where you entered the chamber is another door; the Hook opens it, leading back to an earlier section of the caverns.

Save once you're back in the cellar.

With Pregzt destroyed, every threat in the house is gone — nothing left to fight, only the house's own hazards (a bad fall, a bottomless gap) if you're careless. Head to the main doors and walk out of Derceto for good.