Poseidon's claims were immense. To him, Alexios didn't belong anywhere but the lost city of Atlantis as the Dikastes. His new role would have him guide Poseidon's people to truth, and allow the sixth Isu sense to teach him a real mastery of the Staff.
The codex you need to get to is at the top. You have to climb up there.
You can climb the "blue thing".
Go back down, and talk to Poseidon. He will introduce you to your first tasks as Dikastes.
Rewards: Legendary XP, Staff of the Dikastes (Legendary Staff)
