It is in Sternum, about 31 steps north of the spot the map marks with that name.

And 1 down from the surface once you are there.

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

• Level 35 at least — there is a level door on the way in.
• Key 3142: 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 demon skeleton, elf arcanist and beholder — they live down there.

The chest is 1 floor under the surface. Going down over it, this is what each floor uses:

1. Ground: down through a hole.

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

• 1 — the chest
• 2 — the chest

The strongest 14 of 30 kinds whose nests reach this place.

There are 2 chests here under 2 quest numbers, so you can take them all.