Didn't you find Portal 2 maps challenging enough? Well now you can make your own - Valve has released beta Authoring Tools for Portal 2.
As well as single-player and co-op maps, you can use the tools to create skins, models, sound effects and music.
Valve apparently used similar tools to make the full Portal 2 game.
The Authoring Tools contain an updated version of Source engine editor Hammer; an updated version of Faceposer; example Portal 2 maps and instances; and an updated suite of command-line compiling helpers.
Portal 2 took top honours on Eurogamer - 10/10. "It's never less than a pure video game but it's often more," wrote Eurogamer's Oli Welsh, "and it will no doubt stand as one of the best entertainments in any medium at the end of this year. It's a masterpiece."