The Niantic Project (AKA Ingress)
So, according to this game, reality is not what it seems. Portals are hiding out in plain sight, invisible to all but a few special people with the proper tools (being a Android smartphone and an invite in to the game). The ARG component is being pretty heavily pushed for the plot, but the actual game itself is basically a GPS-based game where certain locations are "tagged" as having portals. They seem to be largely places historical significance, plus post offices and libraries (in-game, the reason for that is something about how XM reacts with the human mind. Out of game, it's because they're the easiest significant sites to get geo-tagged information on, I bet).
Interesting is that the creators of the app (Niantic Labs@Google) have only created two things: Ingress, and Field Trip, an app that shows you interesting and significant historical or cultural events that happened near you. I wonder which idea begat which.