Oh! You know, I actually think you'd really like it. It's kind of like a treasure hunt.
People hide little boxes of trinkets (which aren't supposed to be cursed, in fairness to me) and then there's an app where they can mark down the location coordinates, and others have to navigate their way to it with GPS. You can take one thing as long as you trade it out for something else around the same value. And there's usually a logbook where you can write in your name and the date and everything. Then you put it back for the next person to find.