Geocaching basicallly is combination within an outdoor activities; walking, cross country, hiking, MTB, 4WD, orienteering or navigation and completed with cache or treasury. I've been doing most of them since I was in college, but then now completed by geocaching stuffs, ethics and international forum.
It is fun, challenging, give more reason to go outdoor and addictive specially for those who love being outdoor. Since i join a couple days ago i have been found 6 caches which is apparently scatered around Pilbara region, Western Australia. Bit envy to the cachers who has achieved thousand of caches around the world.
For detail brief of what is Geocaching, you can have a look to this officially video from Geocaching.com.
Enjoy and give try!