Here's a spin off version of the mini game 'PORTAL Which will ship within the Retail version of 'HALF-LIFE 2 The Orange Box' out on the 19th October. Have fun as you decipher a way out of the puzzles using two of these so called 'Portals'. One an entrance, the other your exit. This is a blast and should provide a challenge as you progress. Anyway, read the ingame instructions and see if you can figure out the individual levels.
PORTAL