This occurs during your second Dark Prince transformation (this is in the large courtyard right before the first chariot sequence). In the corner of the courtyard, there will be a hole in the ceiling that respawns enemies until you leave the area. Near that is a panel you need to stab and hang from to open the exit. Climb the closest pole to the hole in the ceiling and a female voice will start announcing sound credits for the game.
During gameplay, pause and input UP, DOWN, UP, DOWN, LEFT, RIGHT, LEFT, RIGHT, X, Y, X, Y.