The Portal 2 Perpetual Testing Initiative has begun, which is Valve's way of saying that you can now make spiffy Portal 2 levels using an in-game map editor.

This free DLC is only available on PC and Mac, and while Valve hasn't commented on whether or not these features will be coming to console I wouldn't exactly hold your breath. Speaking in an interview with NeoGamr, however, Valve did comment that the game has sold over four million units.

The just-under-a-gig update will trigger next time you launch Steam. If you left your computer on overnight you've probably already got it.

I've had a quick go and it's a remarkably simple tool that still manages to feel like a powerful piece of kit that really smart people might use. The in-game editor presents levels in an easy-to-understand block view, and you can even zoom into the levels and test them on-the-fly without ever exiting the game. It's a far simpler proposition than wrestling with the mind-boggling Hammer editor, that's for sure.

I genuinely feel like the bottleneck is now my frankly Neanderthal brain and poor understanding of basic logic rather than my comprehension of the editor, so bravo Valve.

The Steam Workshop integration is pretty impressive stuff, too, and it comes pre-loaded with some excellent examples of what the editor can actually do.