When you are in the tomb with the infinite doors near the end of the game you need to find the correct sequence of doors to progress. The way to do this is to go into landscape view and begin with the door which has the face above it and go clockwise in the following order:
1. 4th door from the entrance
2. 7th door from the entrance
3. 3rd door from the entrance
If you have done it correctly you will be taken to the second level of this room which you navigate the same way. The order now is:
If you start a new game and stay on the balcony and hold L3 and quickly press X, Square, Triangle, Circle, Triangle, X, Square, Circle you will enter the first level of the original 'Prince Of Persia' game. This feature has been redone in 3D and once you get your sword and see a picture of the developers you have completed it.