Geocaching is an outdoor sport where you search for tupperware boxes hidden under rocks with the aid of a GPS navigator. This is a device the size of a cell phone that listens to microwave transmissions from US navigation satellites to calculate its position. The accuracy is currently at best about four metres. Simple but functional models can be had cheaply.
The tupperware boxes are cached by other participants, and you get their coordinates off the net. They contain guest books and cheap little trinkets to trade: my seven-year-old son usually brings marbles. Great geeky outdoor fun for all ages: you get to visit some incredible places, often just off the road you travel daily.
Finding a geocache isn't as easy as it might seem. The cumulative errors of the two navigators involved (yours and the one used originally to pinpoint the position of the cache) mean that it can take repeated visits to find a cache, particularly in woods where reception is bad and in sloping terrain where a few horizontal metres translate to several vertical metres.
Another complicating factor is that you need to solve puzzles to get the coordinates for many caches. For instance, the web site may give you the coordinates of a statue, where you need to note the year it was erected, and do some math with these figures to find the coordinates of the actual tupperware box.
Or there may be several steps to a cache. One of my favourites is a cache where I first had to read a partially encrypted message written with 8th century runes, giving me the coordinates of a tree on a desolate hilltop. Climbing the tree, I found a small knife hammered into the trunk, with a further set of coordinates carved into the handle. These coordinates led me to one of the steep sides of the hill, where I had to climb up and down for ages before finding the cache on a small ledge halfway down. Add to this that I was accompanied by my two-year-old daughter on this particular cache hunt, and you'll see why I'm pretty pleased with myself for finding the box on the first try.
Geocachers refer to non-geocachers as muggles. Muggles sometimes mistake geocachers for drug dealers, gay cruisers or burglars. I've got a good story about that, so stay tuned.
[More blog entries about geocaching, gps, Sweden; geocaching, gps.]