Successfully complete the game to unlock the "Same Bat-Time! Same Bat-Channel!" bonus level. Go to the Batcave's main room, and fly up to the elevator with the Bat-logo to the left of the Batcomputer. When in the trophy room, fly to the far right to reach the studio set, which looks similar to the Wayne Manor study in the 1966 Batman TV show. Switch to Batman or any character with a grapple gun. Pull the grapple point to the left of the bookcase to reveal a secret passage. Slide down the pole to start the bonus level.