Found inside Echo Cave dungeon. Outside of the cave you can expect a camp full of zombies. Zombies do not pose any threat when they are alone, but when they are grouped they can be hard to defeat (if you are there solo). There are several groups of three zombies inside the cave. Use range attacks to kill at least one of them before they reach you. Collectible is inside the last room.
Camp outside Echo Cave.
Echo Cave entrance map location.
Zoomed out map view of the entrance.