Recommended LV: 2
Available after completing “So It begins”
Head to the Temple of Zeus southwest of the town of Sami and talk to the priestess to start the side quest. After the conversation, call Ikaros and have him fly over the Melissani Cave to the north. Have him scan the flooded cavern to mark two objects of interest there. Since you’ll be exploring a cave, having the Revelation skill will be really useful in finding resources and marking enemies.
Cancel the view and dive to the cave. Don’t worry since the water is deep enough for a high-altitude dive. Loot one of the two treasure chests in the area then don’t forget to pick up the Ainigmata Ostraka (Bottomless Lake) nearby as well.
Once done, swim back to the surface and head inside the flooded tunnel. Dive and continue forth to the other end of the tunnel. Don’t worry since there are no monsters or threats here and Kassandra can hold her breath long enough for you to reach the end of the tunnel. The luminescent jellyfishes will be your marker.
After leaving the water, actively use your Revelation skill and ping for ore deposits. There are enemies waiting further inside the cave so crouch and carefully approach them. Deal with them as you please then loot the treasure chest nearby to get the Spear of Kephalos (quest item). This is the 2nd treasure chest in the area so the Melissani Cave will be marked as completely explored.
The walls of this cavern has several ore deposits so take your time in collecting all of them since you’ll probably won’t have any reason to go back to this cave anyway. You also need to reach the vines overhead to continue forth.
There’s one guard waiting at the top ledge so take him out then crawl through the narrow hole and take out the last enemy waiting ahead. Collect the last few ore deposits in this tunnel and exit the cave.
You’ll be back outside behind the temple itself. Loot the nearby containers and report back to the priestess. You’ll have the option to ask for a reward, donate the spear, or lie that you didn’t find it. This is one of the permanent decision points so make sure to decide what you want to do. After choosing your reply, the mission will be complete.