On the title screen press start and pick the option "SOUND TEST". When you're in the sound test screen press X+Y+Z and a little piano will key out the tunes.
Gold Badges
Beat a parallel and wait until the credits have completed. Answer "Yes" to save your game. A gold roman numeral badge for the parallel that was beaten will be displayed.
Mine Cart Views
During the mine cart race in parallel 2, press R to switch to a first person view. Press L to return to normal.
Two-Player Mode
Beat parallel 5, and enter it again. The fighting tournament will now support two players.
Unlockables via parallel
Unlockable
How to unlock
1st parallel
Get to the ship captain's quarters after 4:30.
2 player mode
Beat the 5th parallel and the fighting tournament will be 2 players.
2nd parallel
Get there between 3:30 and 4:30.
3rd parallel
Get there before 3:30.
4th parallel
Happens right after 3rd parallel.
5th parallel
Get there before 3:30 and 4:30, but lose the fight.
Cheat...