[I've been meaning to post this for weeks now]
sf0.org has to be one of the coolest ideas I've seen in a very long time. It's a game, of sorts, or is it? It's played it on the web, but (nearly) all of the tasks are things in the real world. It's a "new interface" to San Francisco, one with more affordances and fewer hinderances "like fear, lethargy, and the police."
It's three parts game, one part scavenger hunt (but read the sign in the first picture), two parts performance art, one part (a)political action, and a healthy dash of subversive protest. Roll that into a tight paper, light it, and you get an explosive firecracker (why, what type of paper were you rolling in?) of pure genius!
The genius is twofold: first, all but the absolute lowest lowest level tasks require you to explore your environment. More than that, they require looking at it in ways you wouldn't normally. Second, most of the tasks require more than one active participant.
The tasks also start relatively simple (upload a photo of
yourself your character, find your celebrity dopplegänger) but they slowly get harder, and in many cases weirder, more elaborate and more subversive. An early task sets this tone: you're supposed to keep track of any money you spend while playing the game. You lose 1 point for every dollar you spend.
Still unsure about joining? Take a look at this flyer for the, erm, party they're throwing. Try to tell me it doesn't sound intriguing. What's that? Yeah, I thought so.
EDIT: Hey, Chicagoans! I forgot to mention this earlier, but the founders of this game started in Chicago, but it never took off. That being said, there's a large contingent of players in Chicago (and Minneapolis for some reason). Many of the tasks are not specific to SF, or can be generalized. You should try it, too!