It is in Stonehome, about 110 steps north 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 80 at least — there is a level door on the way in.
• Something for demon, behemoth and dragon lord — 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. 2 down: down through stairs.
4. 3 down: down through stairs.
5. 4 down: down through stairs.
6. 5 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, 2 down
• → — the treasure lies this way

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

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

• 6 — stairs, 5 down
• → — the treasure lies this way

• 1-4 — the chests

There are 4 chests here under 4 quest numbers, so you can take them all.