The Achondar.

This is really a spoiler (as is the Gorgor videos), because the first time you play Outcast, you really do not expect something like this. The effect it had was really great!

However, the game is 9 years old, so I guess it's OK with a spoiler?

A bit of info on this fantastic game:

Outcast is an action-adventure computer game by Belgian developer Appeal, released in 1999.

Instead of an hardware-accelerated graphics engine, Outcast used a purely software-based combination of voxel and polygons. Makes for much more interesting terrain, at least at the time. I think (pretty sure, well, damned sure actually) they also used voxels for many buildings, walls, trees and stuff. An ingenious use of voxels!

The music has to be mentioned too:
Outcast features a high-quality orchestral score performed by the Moscow Symphony Orchestra and choir. Fitting beautifully with the gameplay, like in a great movie!

The story and execution is simply brilliant! Too bad Outcast 2 was cancelled.. this game was unfortunately never a hit, and the company went backrupt while developing the sequel.

(Some info taken from Wikipedia: Outcast game)