Bonus Play
To Start a new game with all Weapons/Magic at the levels you completed the game at, simply save your game and start a new game. Choose the Bonus Play option and you can start a new game with all your weapons/Magic at the levels you beat the game with. You can only choose the Bonus Play option on the difficulty you've beaten the game on. They will be marked by a sword on the New Game screen.

Sex Mini-Game
A little while into the area of Rhodes, the first area of the game, you will drop down into a bath-house/sauna type area. Instead of continuing and diving down, jump out of the water onto the area around it. There should be two screens which are breakable. Behind one of the screens are two topless women. By walking up to them and pressing the circle button, you initiate the sex mini-game in which you complete a series of button presses. When you have won, you will receive a large amount of red orbs and some green orbs. You can only receive the orbs once, however you may play the mini-game as much as you'd like.

Secret: Now I am become Death... message in the sky + extra red orbs
Hall of Atropos - Upper Level - Do this AFTER the fight with Perseus. You are outside after defeating Perseus. Go back inside through the upper left door. Once in the chamber jump up on the ledge against the back wall but don't go out on the balcony just yet. To the left of the exit, in a dark area where it's pretty difficult to see there is a small star on the ground. Stand on the star and hit R1 a few times (though once is enough). Now run outside on the balcony. Around the corner to your right and under a window there is a second star on the ground. Stand on the star and hit R1 a few times (again, once is enough). Now keep going and quickly grapple across to get over the other side of the roof. Run around the corner and go all the way to the pressure switch, stand on the switch to activate the roots walkway. When the roots are nearly fully extended slow time with the Amulet of the Fates and quickly run across. Once on the center platform you will see the third star on the ground by the first tree. Hit R1 and the camera angle will shift and the following message will appear in the sky: "Now I am become Death, the destroyer of worlds." As the message slowly appears in the sky a few thousand red orbs will also be given to you by the tree you are standing next to. The quote in the sky is from the Hindu scripture, the Bhagavad-Gita. It was later famously quoted by the American physicist J. Robert Oppenheimer to describe the first nuclear bomb test on July 16, 1945.

CREDIT : GAMESPOT