Ui Neill Artifact - South of Benn Uava
This artifact is found in a cave south of Benn Uava synchronization point. You’ll need to head to the small camp near the river and grab the oil pot to explode the breakable stone barricade blocking the entrance into the cave. You won’t want to throw the pot as the tunnel into the cave is small and it’ll hit the ceiling before it hits the barricade. Instead, place the pot near the door then shoot at it from outside the tunnel. If you need arrows, there are a few stuck in a nearby log. Once you’ve exploded the entrance you’ll be able to grab the artifact from inside the cave.
Ui Neill Artifact - East of Donegal
This artifact can be found in a cave east of Donegal monastery. The entrance into the cave is surrounded in a green poisonous fog and there are also several pots in your way. You’ll need to quickly pass through the fog and break the pots to reach the small room at the back of the cave where you’ll find the artifact.