Not very colossal cave, a game for the 'require sound' assignment by Colin Fralick, with sound effects from soundjay.com.
The idea behind this game was for the player to be blind visually, with the ability of echolocation to compensate. He would have to find his way to the end of a maze, testing the walls with sound to determine the layout of the area and playing "marco polo" with an NPC helper (who can be called to the player's side at any time) to keep his bearings.
The basic implementation was more or less straightforward. The player moves around a grid, some squares of which are marked as "walls", forming the maze. He is blind, but can "ping" the area ahead of him to determine how far away a wall is in that direction. It would be easy to become disoriented like this, so I added a stationary NPC helper as a reference point as well.
The idea of an echolocating player character is interesting because it forces the player to navigate the world using a sense not normally used for navigating. Other than that, gameplay is familiar and simple out of necessity.
I found OpenAL's 3-d sound, or at least its ease of use in figuring out 3-d sound, somewhat disappointing. Obviously for a game that relies on directional sound like this one does, simple stereo is not enough, so the game mechanic I tried to implement does not work at all. Aside from that, the few elements that do not rely on directional sound, like the variable delay in echolocation, worked well, and I feel the game would scale well to something larger.