This stage is basically all about going up. For the most time you will be following a trail of blood or a blue flame, meeting various characters on your way.
Head towards the chalice.
Afterwards follow the red line, pay a visit to your family and move on.
This way you will reach a dying Pandora, who will change into blue flame of hope.
Move on and you will see your family, brutally murdered. Continue going up the screen after the cutscene ends.
You will pass by Athena. As you walk away the camera will once more show her body [RS] - return to her.
Go straight in the direction of the pit and Kratos will perform a characteristic jump, known from the first game.
You will land in an ocean of blood. Swim towards and flame and then swim around while getting away from the voices of the gods you've killed.
Another source of light will appear in the distance. Swim towards it and you will find yourself in front of the Pandora's Box. Open it to end the stage.