An ARG is an interactive narrative in which players work together to solve puzzles and co-ordinate activities in the real world and online, using websites, GPS tracking devices, telephone lines, newspaper adverts and more. All of which sounds like it must require even more effort and resolve than a bank holiday gym session, but ARGs employ media - text messages, blogs, social networking sites, video-sharing - that many people already use on a daily basis.
I also explained it today as...
"It's similar to a MMORPG (Massively Multiplayer Online Role Playing Game) and a LARP (Live Action Role Play). These are games that have existed for years separately and only now as we find ourselves with man-portable internet-connected GPS-aware devices can we attempt to add mix them. Essentially it's a puzzle game that you have to walk around to solve. I want to add actual multi-player and humanocentric role-play to the concoction. It is larp-esque. But it also allows a form of gaming when just out and about. Some games may end up being played solo and some will require interaction. And some of the puzzles can be incredibly elaborate.
i.e. a 'password' that consists of a GPS location and a photograph that must be matched in position. GPS gets you within maybe 50 metres, then you find the position to map the photo. The photo might be a silhouette of a landscape or the light through yonder window. Once the correct combination has been discovered, the application can then deliver the package - be that text, an image, a movie or an audio sequence.
i.e. a set of ten cards containing a QR code sits in a till at a local bar. From a combination of previous clues, you have been directed to ask the bartender for a card with a number on it. You take a picture of the QR Code and it reveals a clue which is relevant to your story. The wrong card will likely lead you down the wrong path or, in a good ARG, bring you down a side path of the game you are currently in.
So in effect you tie it to a location, a perspective and if natural light is needed, a time..."
I see a lot more possible.