Its a high tech treasure hunt. You hunt for caches (they range from ammo boxes and a little bigger all the way down to 35 mm film containers and smaller) that are hidden all around the world. I think there are currently 1.3 million hidden around the world. You go to
www.geocaching.com and find ones that are in your area or where ever you may be going and upload them to your GPS. Inside the caches are a log book to sign and if they are bigger ones they have small items inside that you can trade for (which kids love to do so bring a few small trinkets to trade). Some of them can be VERY hard to find as people cleverly hide them. Geocaching is a very fun thing to do with the family as its gets the whole family working together for a common goal. Some of our favorites are the ones inside of cities because they have to be hidden very well so other people dont see them and take them. Geocaching has taken us to many places in our area that we never knew about. Some are at a historical location or a place in a park you never knew about. I have a Delorme PN-40 that I use for hunting and ice fishing that works great for geocaching. With the GPS that I have has a feature that lets my download lots of caches along with all the info on them so I can read the notes while im in the field. I just bought my wife a Magellan Explorist GC for her birthday and were getting ready to go try it out so she can get use to it before we leave. Even if your GPS doesnt let you upload into you can punch in the coordinates. We first started using our garmin from the car and it got us by until we figured out that we really liked geocaching and purchased a better gps. Check out
www.geocaching.com and that will explain it a lot better. Its a really good time and gives you a reason to get outside in nature and have a good time. My wife found 3 our first day and have been hooked ever since.