Natural luge tracks are tracks that are used for naturbahn (from the German "natural track") luge competitions. Tracks are often located along mountain roads and paths. The track surface is made of packed snow and ice, with a slope of not more than 15%. Unlike its Olympic counterpart "kunstbahn" (artificial track) luge, natural tracks are to be adapted to the natural conditions and artificial refrigeration and banking are prohibited.
References
List of natural luge tracks Wikipedia(Text) CC BY-SA