The Elfstedentocht (; West Frisian: Alvestêdetocht , English: Eleven cities tour) is a long-distance tour skating event on natural ice, almost long, which is held both as a speed skating competition (with 300 contestants) and a leisure tour (with 16,000 skaters). The Elfstedentocht is the biggest ice-skating tour in the world. The tour is held in the province of Friesland in the north of the Netherlands, leading past all eleven historical cities of the province. The tour is held at most once a year, only when the natural ice along the entire course is at least thick; sometimes on consecutive years, other times with gaps that may exceed 20 years. When the ice is suitable, the tour is announced and starts within 48 hours. The Elfstedentocht has been declared to be in danger of "extinction" due to climate change. In the past 50 years, the Elfstedentocht has taken place only three times, most recently in 1997. Course and rules The tour, almost 200 km in length, follows a closed or circular route along frozen canals, rivers and lakes visiting the eleven historic Frisian cities: Leeuwarden, Sneek, IJlst, Sloten, Stavoren, Hindeloopen, Workum, Bolsward, Harlingen, Franeker, Dokkum, then returning to Leeuwarden. The tour is held only if the ice is, and remains, at least 15 centimetres thick along the entire course as about 15,000 amateur skaters take part, putting high requirements on the quality of the ice. The last tours were held in 1985, 1986 and 1997. All skaters must be members of the Association of the Eleven Frisian Towns. A starting permit and bib is required (€100 in 2017). Skaters must collect a stamp in each city, and at three secret check points, and must finish the course before midnight. There are often points along the route where the ice is too thin to allow mass skating; they are called "kluning points" (from West Frisian klúnje meaning to run on skates over a carpet), and the skaters walk on their skates to the next stretch of good ice. In 1997 ice-transplantation was re-introduced to strengthen weak places in the ice, for instance under bridges. The finishing point of the Elfstedentocht is a canal near Leeuwarden, called the "Bonkevaart", close to the landmark windmill, De Bullemolen, Lekkum. Route table Planning and publicity Since the Elfstedentocht is such a rare event, its declaration creates excitement all over the country. In the build-up to