Aura is a game where the player must navigate through mazes guided only by sound cues -- no graphics whatsoever (if you write me saying "I tried Aura out it didn't work, all I got was a blank screen" then you've missed the point of this game).
This game is quite a bit of an experiment. Though other audio-only games and mini-games have come before it, the field is still very new and Aura is possibly the most ambitious game of the sort.