5 0 0Actions This one's is quite easy, you have to go back to Kephallonia (after killing the Cyclope) and start killing goats until an Obsidian Eye Fragment drops. It drops randomly and you can get it by killing second goat as well as a 50th.
0 0 0Actions The game might be a little stubborn and take a while to drop the eye, if that's the case just save and fully close the game before launching it again, it should then drop soon after.