If for some reason you haven’t played Valve’s short but incredibly sweet puzzle game Portal (say, a four-year coma, for example) then there really is no better time to pick it up. Valve is offering it to you for the price of… on the house.

You’ll have to be quite quick about it though, as this free Portal offer extends only until September 20. Still, I’d say that four days is enough time to download it, it’s only little! It’ll take no time at all.

Portal was the surprise smash hit of late 2007 that Valve put out as a half/experiment, half/apology for the long, long wait for Half Life Episode 2. Nobody expected this offcut of the Valve development team’s efforts to blossom into such a huge success, both critically and commercially.

Like I said, it’s short with probably around 2 hours worth of content (adjusted up or down according to your level of puzzle-cracking power) but they are 2 hours of gaming where every second is worth savoring.

As this old teaser trailer demonstrates, you use your portal-generating gun to solve a set of increasingly fiendish puzzles set by a ruthless artificial intelligence program. If you have a logical mind that loves to experiment, then you’ll fall in love with the physics system presented in Portal.

Even if you’re not all that into puzzle games, you really ought to give Portal a try. You might be pleasantly surprised and if the gameplay mechanics don’t get you hooked and wanting more, the humor almost certainly will.

It’s Friday, after work ends, do yourself a favor and download this game. It’s free, it’s funny, it’s eminently lovable and I think that it’s worth mentioning again that it’s free. There is literally no reason good enough to stop you from taking 2 hours out of your weekend to download and play Portal.

This is a Steam exclusive offer available for PC and Mac. Download Portal for free here.

Still no word about that free Portal 2 DLC due for mid-September though. Come on Valve, you’re killing us!