According to the Red Shoe Diaries, this is a concept art for Red Sands, but obviously does not fit at all with the name. Lava? Robotic buildings? Most likely a concept from later on.

This is the concept image for Crystal Frost Zone, despite the winter look to it, it looks nothing like the final level.

This is the only avaliable image of Crystal Frost Zone, most likely the beginning of it. Looks like something straight out of the 'Bug!' game. That appears to be a 'Litebug' to the right of screen.

This unknown level was upsized in the Red Shoe Diaries, and looks similar to a castle. Green Coloms are everywhere, and almost looks like mirrors are surrounding the area. There is one Trilldrill attacking Sonic, but two of one unknown badnik floating around! It's also green, unlike the other enemies we know about which are red. Clikc the image for a larger version.

Another unknown level using a lot of bright, 'trippy' colours. To the left is what appears to be a low polygon Pharoh statue. Could this be a part of the Red Sands? Click the image for a larger version.

Here Sonic walks through a very dark section of land. A Balldron is shooting at Sonic, as well as the background being similar to some of the Galaxy Fortress level images, but the level itself looks nothing like it.

Sonic's jumping through a level which doesn't look at all like anything from any other levels. It seems more detailed and very un-Bug!-like.