Any of ya'll do this? Just started today with my 10 year old. Pretty fun, basically a log sheet hidden in some sort of cache like a little metal pill box that you have to find using gps coordinates. Once you find it you write your name in it and log your find on the website. My son is super stoked on it, we had a fun first day finding 3 of them all within walking distance of our house.
http://www.geocaching.com
http://www.geocaching.com