Geocaching is not for the casual urban adventurer. The concept is simple enough – seek out a hidden treasure by following a specific set of GPS coordinates – but there's a reason why it never caught on in the mainstream. Not only does it command a giant commitment of time and energy, but there's also a pretty steep learning curve for new users. Wonderground is geocaching for the rest of us. Created by General Electric (yes, that one), the scavenger-hunting app challenges users to explore their favorite cities with the promise of the ultimate reward: Knowledge.