It is in Trollcaves, about 48 steps south-east of the spot the map marks with that name.

And 3 down from the surface once you are there.

• 1 — Trollcaves, as the map itself names it
• 2 — the ground above the treasure

• Key 4901: a locked door bars the way, and that is the number of the key that opens it.
• Key 4903: a locked door bars the way, and that is the number of the key that opens it.
• Key 4904: a locked door bars the way, and that is the number of the key that opens it.
• A rope. You drop in through a hole, and a rope is how you climb back out.
• Something for giant spider, beholder and slime — they live down there.

The chest is 3 floors under the surface. Going down over it, this is what each floor uses:

1. Ground: down through a ladder.
2. 1 down: down through a hole.
3. 2 down: down through a hole.

• 1 — the way in: a ladder, ground
• → — the treasure lies this way

• 2 — a hole, 1 down
• → — the treasure lies this way

• 3 — a hole, 2 down
• → — the treasure lies this way

• 1 — the chest
• 2 — Thais Northdungeon

One chest, one reward.