Does anyone else geocache?
http://www.geocaching.com/
I did it fairy extensively before my daughter was born and then subsequently found civ. The basic premise is that people hide these "caches" out and about in the world. They record the latitude and longtitude and publish those coordinates with a description of the cache, cache's location, etc.
I've hidden a few around my local area, and also found quite a few (~ 67 so far). You need a GPSr, but you can get those relatively inexpensively (< $100) unless you want one that will hold road maps as well ($200 - $1000 depending on size and other features).