You can get to the Debug Menu from anywhere in the game. To activate it press [START] to active the sonar map. Then press the following buttons: [LEFT], [1], [2], [1], [2], [DOWN], [2], [UP]. You will be in a menu where you can select any level, get Invincibility, play music and a lot more!
Table uses following format:
Stage : Password
Vents of Medusa : EAACC
Maze of Stone : EABDC
Sea of Darkness : EECAC
SkyWay : EEECK
Tube of Medusa : DAFDL
DDD Swimming : CEOAI
Getaway : BIRFD
Asterite Cave : ECKQA
The Eye : (You get different passwords after saving more globes)
HGPQA , MCDDK , JSFGK , BDKQE , JQDCG , MSDHG , GNTHP
Dark Water : (You get different passwords after saving more globes)
MUGMK , JJVAL , EIOWI , JWAJK , GIOUM , VAJPN
Sea of Birds : FJKGE
Convergence : MGGOG
Vortex Future : IADSH
Globe Holder : DXJGF
Convergence : DQLWF
DDD Swimming : RODCM
New Machine : NFHWP
Vortex Queen : FGXMO
DDD Swimming : FGVKO
Atlantis : JJDSP