The Cut Mineshaft Level (unofficial fan-made name) is a level set inside a giant cave with a mineshaft going though it that was supposed to appear in the original Crash Bandicoot Game. The level can only be seen in the concept art for the game by Joe Pearson. It seems to be the basic inspiration for Koala Kong's boss fight area in the same game, but it could be also related to the cut lava level mentioned by one of the developers of the game.
Nothing is known about this level. Gameplay-wise, Crash may have ridden in a minecart along a track, having to avoid obstacles, much like Compactor Reactor and Ghost Town in Crash Bandicoot: The Wrath of Cortex.
The mineshaft appears to be very detailed, with waterfalls and lakes, crystal stalactites, cauldrons of lava, and stone idols.