Here is the full list of all 20 Argonus and the Gods of Stone achievements.
Talk to three gods.
Talk to two gods.
Talk to one god.
Find all the broken pieces of wrecked ships.
Find and place all the mosaic pieces.
Light all sconces and braziers.
Unearth a certain ancient skull.
Obtain every takable object on the isle.
Read all journal entries.
Ride a stallion three times.
Steal two things from their owner.
Complete all Achievements.
Talk to four gods.
Talk to five gods.
Talk to every god on the isle.
Raise the dead.
Teleport to and from every temple on the isle.
Set free the souls of all the Argonauts.
Set free the souls of all the isle's inhabitants.
Learn to use a forge.