Battlefield Loot (Hidden Treasure)
At the northernmost of the three hidden treasure icons on the map on the islands to the west of Oxenfurt outside some spiked perimeter fencing guarded by a Water Hag.
When you reach the location and have cleared it out, use Witcher Sense to find the dead body outside the walls sporting a red glow. Loot the fellow’s body here for a Crumpled Note and a Key attached to a Crumpled Note– this will activate the side-quest ‘Battlefield Loot’.
Read the Crumpled Note in the Key Items section of the inventory. This will update the objectives.
Activate Witcher Sense and follow the blood trail here a short distance until you reach the remnants of a wooden guard tower behind the ballista. The trail ends here. Use AARD to destroy the barrels at the base of the tower to reveal a chest behind them.
Use the key on the chest here to complete the side-quest.