O-Ringen is the world's biggest orienteering adventure, with participants from all over the world. It is held annually, during a week in the end of July and is located in a different part of Sweden each year. O-Ringen is a meeting place and a folk festival for an average of about 18,000 orienteers who make around 80,000 starts together during the competition week. The participants come from all over the world and about 40 nations are usually represented. World elites and ordinary exercisers participate in over 100 classes, from the youngest of the 10-year classes to the real veterans 95 years and older.