Thanks for the great suggestions and links everyone. As always, there's a wealth of awesome ideas around here! Scavenger Hunts, sundials, geocaching, orienteering, cartography, burried treasure.... Thanks for helping me take it to the next level!

Geocaching is something that I want to find out more about. Am I right in my assumption that it's GPS driven? I don't own and have never used a GPS. Any suggestions on how best to get started?