Hey,
I remember having played on a downloaded maps long ago and I forgot the name, if someone could know and tell me the name of it that would be amazing!
It was a sort of "'demonstration" map, not really a multiplayer map at all. You standed ontop of a sort of square and the map completely made abuse of the Warp / portals to make it look like you were ontop of a giantic sphere, like a planet. There were sorts of chandeliers hanging on the ceiling that balanced slowly, and a very weird atmosphere.
Does that ring any bell ?