HEART OF GAIA
Your goal in this area is to get on top of Gaia again. Start off by dragging the a big post on your right (look for the glowing object) to the shallow space to the left. Rotate it first with the vines facing you and push it towards the shallow space of the wall.
Start climbing up and make your way through Gaia. You will find Sentries here that you have to kill. Once you’re all the way up, prepare for a boss fight, this time it’s Poseidon.
BOSS 2: POSEIDON
See the claws holding Gaia? Attack those legs to get it off from Gaia. Watch out for the electric current that Poseidon will do on the ground. Dodge it by rolling around. Once you get those claws from Gaia, you will see a scene again where you will have to face Poseidon.
You can finally attack Poseidon head to head. Do not approach him too quickly because he has some attack that you need to watch out for. His trident will cause the ground to have an electric current but if you roll right, you can attack him directly. Once you deal a decent amount of damage to him, get on top for a QTE. This time stab his heart!
Back to Phase 1, do the same thing. This time, Poseidon will launch three claws on you, so dodge it! Once the legs are off Gaia, you’re done! Just do some QTE event and watch how amazing it is.
God of War III Walkthrough: Prologue- Poseidon,