To start, go to the far southeast corner of An Skellig to find the hidden treasure marker, a body on a wrecked longboat. Note that there are a couple sirens in the vicinity so you might have to deal with them first. Loot the corpse for the cargo list and read it to learn the location of the treasure is just southeast, out in the ocean.
Swim out to the area and you'll find the chest on the sunken boat here, near the other end of the boat.
Journal entry Edit
- While traveling the world in search of Ciri, Geralt happened across a barely-legible document which made mention of a mysterious treasure. The witcher decided to take a careful look into the matter.
Four barrels of salted herring
- -8 barrels of drinking water
- -3 barrels of vodka
- -5 barrels of whale blubber
- -4 bails[sic] of fur and rabbit pelts
- -1 chest of various treasures, worth a sum total of one thousand Nilfgaardian florens.
- The chest is sealed. If the seal is found to be broken upon delivery, no payment shall be issued.
- His instincts did not mislead him. Geralt found the sunken ship, and within it - a chest full of valuables.
- Read the notes you found.
- Find the sunken treasure using your Witcher Senses.