You will once again arrive in the well known room, this time able to collect all the experience chests and one with w power-up [!!!], hidden in a alcove next to the chain (not the one you've been climbing). Once you open them all, go up the round stairs.
Approach the Pandora's Box and begin to move the crank. This time you will be able to push it till the end, which will start a cutscene.
After it ends, the first fight with Zeus will begin. It will be kept in a 2,5D style. You will be able to move in one line only, so dodging the enemy's attacks will be much easier.
During this phase Zeus will most likely attack with lightning bolts after jumping. Avoid getting hit by simply jumping in the other direction.
Additionally the highest god will attack you with combos. They're not very effective, as you would have to stand very close to him for a long time to even get hit. Zeus can also sometimes break your combo in the middle and attack.
During the fight Zeus can sometimes grab you and drag you through the whole "arena". Move the left stick to avoid getting thrown at the wall.
At some point a QTE mark will appear above the enemy's head. Grab him and activate an event during which you will have to press three of the basic buttons.
After the first QTE, you will move on to the second phase of the fight. It's not very different from the first one. Zeus will however learn some new moves: attack with a series of lightning from the ground (quickly dodge) and teleport (he'll be able to quickly move behind you).
Deal enough damage and another QTE mark will appear. Quickly tap Circle to complete it successfully.
After finishing the initial part of the fight and watching a cutscene, you will regain control over Kratos. Head to the door and save your game before exiting the ruined room.
Go forward and glide towards the terrace. There you will fight again (and surely not for the last time). It will be really short and easy. For the most time Zeus will try to hit you with lightning. Dodge his attacks and deal enough damage...
... and Gaia will appear. She will grab the whole building and you and Zeus will land inside her.
Before the final fight begins, you will have to follow the familiar path towards the Titan's heart.
Once there, destroy the crystals surrounding her heart and incinerate the vines found there. Hit the heart a couple times and your health will regenerate.
Zeus will join the fun and the last classic fight will begin (you'll have several more occasions to attack him later on). Pay attention to Gaia's heart during the fight, as after regenerating it can be used as a health pack both for you and your enemy as well. Remember about it while playing on higher difficulty setting - you will get green orbs by hitting the organ a couple times). If Zeus runs toward the heart (after charging up and throwing a comment) and starts regenerating, be sure to attack him and stop the process.
The enemy will mainly throw lightning bolts at you and clone himself. However you should always be able to tell the clones from the real ones. By destroying the fakes, you will receive mana and orange orbs which fill up your Rage of Sparta bar.
The god will also be able to quickly dodge your attacks and hitting him won't be that easy this time around. He will move very fast which will allow him to do a quick counter attack.
Hit him enough and a QTE mark will appear above his head.
The QTE will take the form of a mini-game, as before you will be able to push Zeus onto Gaia's heart (where the finishing blow will be dealt), you will have to alternate between pressing L1+R1 and mashing Circle. If you fail with L1+R1, a sub-QTE will launch, during which you will have to press three basic buttons to avoid death.
As you get close to the heart, Kratos will jump into the air and you will have to do a curve with the left stick. Thanks to it Zeus will be pushed onto the place where his death will begin. Press L2 and R2 at the same time.
You will begin wrestling with Zeus, quickly press Circle.
A cutscene will play.
Afterwards you will take control over Kratos once again. Approach the sword lying in front of you.
You will get attacked once again - press Circle to get out of it alive. This will end the stage for now and you will sink into darkness.