X Marks the Spot
Treasure hunt
Skellige suggested level 12 
On the world map
From the journal
Geralt found a key and a map with a location on Ard Skellig marked on it. Though he usually smirked at wild-eyed treasure hunters, he couldn't resist seeing if some treasure lay hidden there.
To his surprise, Geralt discovered the treasure map was neither a joke nor a trap. It truly did lead him to a chest full of valuables.