Caves of Oblivion
The Caves of Oblivion is the fifteenth level (in the official numbering) in Keen 3. This is the next to last required level, as it is protecting the Castle of the Grand Intellect, in the Island of the Grand Intellect. It consists of a big maze of caves inside a mountain, and is probably used by the Grand Intellect to confuse intruders trying to get to his castle.
There are two exits in this level: the normal, hard one; and the alternative, easy one. The normal one is intended to be reachable by navigating through the cave maze, after getting the four keycards; the alternative one can be reached jumping over the mountain. However, as in Hal's Kitchen, part of the level, the last section, is not accessible due to what may be a level design oversight. In addition, a multitude of spikes in front of this door make it impossible to reach. Therefore, the normal exit cannot be reached, and the only way to finish the level is through the alternative exit. Even if it was accessible, however, it most likely would not be worth the trouble; the level is a vast labyrinth with numerous hazards (including a lot of Vorticon Grunts, VortiNinjas and balls and jacks) and relatively few points.
It could be that this inaccessible section is purposeful — as in the story it is said that Keen "will face the impossible maze of the Caves of Oblivion!" This is further evidenced by the sign near the beginning that says, "GO UP" in Standard Galactic.
See also List of Keen 3 levels.