It is in Stonehome, about 143 steps north-west of the spot the map marks with that name.

And 6 down from the surface once you are there.

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

• Level 100 at least — there is a level door on the way in.
• Key 6010: a locked door bars the way, and that is the number of the key that opens it.
• Something for demon, warlock and behemoth — they live down there.

The chest is 6 floors under the surface. Going down over it, this is what each floor uses:

1. Ground: down through stairs.
2. 1 down: down through stairs.
3. 3 down: down through stairs.
4. 4 down: down through stairs.

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

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

• 3 — stairs, 3 down
• → — the treasure lies this way

• 4 — stairs, 4 down
• → — the treasure lies this way

Some floors are not on the list: their way down is further off than the rest, and that stretch you have to find yourself.

• 1-4 — the chests
• 5 — Annihilator Exit
• 6-10 — Annihilator Entrance · tiles to step on

The strongest 14 of 24 kinds whose nests reach this place.

There are 4 chests here and they all carry the same number, so only the first one you open gives anything.