Crash Bandicoot 3: Warped Cheats

To go to the hidden level, Hot Coco, go to Road Crash and drive into the yellow alien sign.

To access the hidden level, Eggipus Rex, go to Dino Might and take the Yellow Gem Path to the secret area. While being chased, let the second pterodactyl attack you. Instead of killing you, it will carry you off to this secret level.