You'll have a lot of fun Feedz.
Dave, Geocaching is basically treasure hunting. People place "caches" anywhere they want, then upload the entry on geocaching.com. The cache can be just a simple log or it can be an actual box with items in it to take. If you take the item, you're supposed to leave something behind.
You download the app on your phone, and you can basically pick whatever cache you want, and the app will load the coordinates of the cache. Usually you only have a riddle or a very brief clue to find where it is. Some are very easy, and some are hard as shit. We couldn't find some of them that were supposedly near a waterfall we found.
It's a really good date idea in general, because you get to go to interesting places and you actually have something to do that will form a natural connection between two people.
It's also a good way to murder your date. Don't tell anybody.