Not sure if many have heard about it but Geocaching is a fun family oriented game that doesn't cost much to get into (Cost of hand held GPS or geocaching app for blackberry or iphone).
Geocaching simply put is "Using multi-billion dollar government technology to look for $1.98 tupperware in the woods".
What we do is hide small items from the size of a thumbnail to the size of a 5gal bucket or larger in places. Could be anywhere from the side of a building to a fake stump in the woods. The most popular containers are old military ammo cans of all sizes as they are sealed and offer good protection and come painted OD Green.
Many are called in plane sight cache where they are camouflaged to blend in to the surroundings. Some you have to do specific things to get the cache. There are even some hidden in the middle of lakes and rivers.
The caches are ranked by terrain and how well hidden they are. A cache that is a 1 terrain and 1 hide difficulty can be accessed by wheelchairs and strollers. A 5 terrain requires special equipment like 4x4 vehicles or it may require you to climb the side of a mountain or repel down a cliff of it may require you to scuba dive for it in a body of water. A 5 in the hide difficulty means it may take you a few hours to find it.
Caches are hidden from California to Main and in just about every country around the world.
Geocaching - The Official Global GPS Cache Hunt Site
is the main web site for geocaching and has all cache placements located on the site. You do have to be a member to view them. There are two levers regular and premium members Regular membership is FREE but you some times miss out on premium member only caches. Premium membership is not expensive at all at $30 a year. Even if you don't like going in the woods there are tons of urban caches in every city in the country.
Great intro video series.