Swim to a statue at the end of the hall and use the grappling hook to get to a crystal, then destroy it - you will restore the time this way. To get further, you have to make both bells sound at the same time. Jump towards the right one (the Chronos bell) and move it by tapping L1 and R1. Slow down time, get back to the central platform and use the battering ram to activate the Zeus bell. If you manage to do it quickly enough, the statue at the center will crack. Now dive and use an underwater lever. Return to the surface and use the turnstile so that the blue crystal gets into place. Use the lever again. You can now rotate the battering ram - make it face the statue, then activate it once more. You can find red orb chests in the following corridor.
You finally face the Sisters of Fate. Your first opponent will be Lahkesis. The battle against her might seem difficult at first, but it gets fairly easy once you master using the Golden Fleece to reflect her projectiles (by pressing L1 in the exact moment a magical bolt hits you). Not only will you deal damage to her by successfully performing this move, but also make her drop numerous green and blue orbs. Chronos Rage is also helpful here. Besides, use short -based combos. Once you deal enough damage to her, she will start to electrocute the floor from time to time. When you see that she's about to do that, you have to use the grappling hook to get into the air (R1). Jump from one hook to another if she's firing missiles at you. When Lahkesis is up in the air, the best way to hit her is still reflecting her projectiles. To finish the battle, execute the fatality when prompted (you have to use one of the hooks to reach her in the air).
After a short cut-scene, Atropos will take you back to the times of the first God of War, to your epic battle against Ares. You can't let her destroy the giant sword that you later used to defeat the god. There are lots of weak enemies wandering around the sword - attack them using your Chronos Rage to gets lots and lots of orbs. You can't run out of mana this way. Use your magic against Atropos herself as well. You might also try to reflect her projectiles with the Fleece. At the end of the battle you will once again have to repeat a certain button sequence.
In the final stage of the battle you will combat two sisters at once. Focus on Lahkesis in the first place. She fights in the same way as she did before, but uses a lot less projectiles, so you have to use your own weapons more. Try to avoid Atropos' energy beams. Whenever you deal enough damage to Lahkesis, stop the time and deal with Atropos. You should be able to break one of the mirrors each time you get the chance to attack her. Repeat it a few times and finish the battle by executing a fatality.
Continue on to the next room, grab the wall and go along the ceiling to get to a balcony on the upper level. If you want to, you can glide to the ledges on the left and on the right for some red orb chests. Go further to see the last Sister of Fate - she's apparently "a little" different from the ones you've already defeated. Smash through the wall on the right and go do along the stairs.
This battle sequence is actually your last meeting with any regular enemies in the game. There's a real handful of difficult opponents to defeat here, and new waves will appear each time you advance one segment. Use the energy barriers that appear from time to time and divide the platform into smaller pieces - when the enemies are split into smaller groups, they are a lot easier to deal with. Save your health and mana and don't use chests if you don't have to - you can always save them for later.
When you finish this bloody marathon, you'll end up near H. R. Giger-inspired gate. Hit the nails of the sculpture and you'll be able to enter.