You can get to the Debug Menu from anywhere in the game. To activate it press [START] to pause the game while Ecco turns from one side to the opposite. He should be looking at you now. Then press the following buttons: [RIGHT], [B], [R], [B], [R], [DOWN], [R], [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
Undercaves : HYNCSRDQ
The Vents : XPRMMZBD
The Lagoon : RKIVVHCC
Ridge Water : -RTGCXGB
Open Ocean : W-QBCXG-
Ice Zone : .YNTCXGS
Hard Water : RFXPCXGV
Cold Water : YC.?CXGQ
Open Ocean 2 : TS-K.WGC
Island Zone : HSXPBXGX
Deep Water : KSWKCXGV
The Marble Sea : R.GGFXGY
The Library : NX:KFXGJ
Deep City : GZPTFXG-
City of Forever : NWBYCXGW
Jurassic Beach : TKGTGTGQ
Pteranodon Pond : F?TXGTGF
Origin Beach : LR:LGTG:
Trilobite Circle : X-WQGTGT
Dark Water : VFCRKTGK
Deep Water 2 : MFXAKNLW
City of Forever 2 : ?STNNTPY
The Tube : BV?!TQPY
Welcome to the Machine : BTWJVQP.
The last Fight : DLHSTQPT
The Stomach : DBBXVQPK