I first heard about geocaching some years ago - now that I have some suitable equipment in the shape of an iPhone I've been meaning to give it a go.
Looking on www.geocaching.com I found that there were numerous sites near us so we downloaded their iphone app and headed out, iphone in hand, this afternoon to find one not too far from us.
The app uses a compass image to give a rather nice direction and distance indication on the screen. This got us to the right area and here the search began. We knew we were looking for a "magnetic nano" but other than the expectation that this would mean it was attached to something metallic we had no idea what we were searching for.
Initial searching didn't yield anything but after a while we found it and discovered that nano does mean rather small. However, despite its small size, it contained a tickertape style pice of paper on which to log your visit. We left our mark (first people to do so in 2011) and then returned it to its hiding place.
Great fun, despite the rain, think we may well have a go at some of the other ones in the area now.