Ruins of the Ancient
This location is located to the northwest, past the Light Elf Outpost and before the cavern that leads to Northri Stronghold. There’s a Soul Devourer roaming the area and a Legendary Chest. The map can be immediately found on the ground, a few steps away from the chest.
The treasure is located in front of the main entrance leading to Fafnir’s Storeroom. This is best done during the favor “Fafnir's Hoard”. The mound is located under the goat’s head and beside the brazier to the left.