There are three unused levels still present within the game; an Airship Level, an unfinished version of Fahrenheit Frenzy, and a Warp Room that was presented at E3 2001. Out of the three, the Airship level is the most finished.

The E3 Warp Room is an area containing 5 warp pads, all of which have no collision and will not warp the player anywhere. Interestingly, each warp pad has a hologram of their respective levels overlaid on the pads. This feature isn’t used anywhere in the final game.

The Airship level and the E3 Warp Room can be accessed through Action Replay codes on the North American GameCube versions.
Contributed by ShyanVixen