Making my way thru the single player

[ronhedlund]

I am a little confused. Right now I am making my way thru the single player part of the game. I am approx. half way thru. The game is really cool. It kind of reminds of the old Hexan/Herectic game. Anyway what is the point of the whole challenge room. Is it a place where you can re-hash old levels and redo them over again. Or is it a place where you can redo the levels and pick up anything you missed or is it just a completely new area of the game? Could some one give me a better understanding of that part of the game.
Thanks