Inside the Old Sord’s Cave public dungeon. Dungeon entrance is located right in the middle between Hermit’s Hideout and Icewind Peaks Dolmen, south of the road passing by those two points of interest.
When you are inside the dungeon, follow the route south. This means you have to keep on going straight at the first intersection. What you are looking for is hidden in the southwestern corner of the next cave room.
Dungeon location on the world map.
In the corner of the room.
Location on the dungeon map.