The chamber21.zip file you have requested: Maps Levels Missions / Portal: Chamber 21 Map - 2.42mb is not available. Perhaps try browsing all files for the game Portal and upload any files you want to share or are missing. This is the only information we could locate:
Chamber21 ReadmeTo install unzip file and place map files into your folder namedSteam\SteamApps\username\portal\portal\mapsto play the map, run portal, open the developer console and type map chamber21 or chamber21advanced then hit enter This map is 100% playable all the puzzles work. With almost no bugs. Although there are a few ninja solutions to some of the puzzles. This map uses the principle of angular portal entry in some of the puzzles.