Don't know if anyone already knows about this, but I've just been told. It's called Geocaching and it's a massive world wide treaure hunt with items/objects hidden in so many places around the entire world. You use GPS/smartphones to locate these tresures and you'll be surprised how many are actually hidden near where you live right now.
This will appeal to game players on here who like doing things like this in real life.
http://www.geocaching.com/