Hold L + R and press Down, X, Up, Y, Down, Down, Up, Up at the main menu. Release L + R and a "Cheat" option will appear at the main menu. Select the "Cheat" option, then enter one of these codes.
Enter 8wonder as a code.
Enter KKst0ry as a code. Note the o is a number "0".
Enter GrosBras as a code.
Enter KK 999 mun as a code.
Enter lance 1nf as a code. Note the number "1" in the second word.
Enter KKtigun as a code.
Enter KKsh0tgun as a code. Note the o is a number "0".
Enter KKsn1per as a code. Note the i is a number "1".
Enter KKcapone as a code.
Enter KKmuseum as a code.
Unlock Artwork Gallery:
Beat the game.
Thanks to Revolution readers Momthra and monkeyman!