The Groundhog Day Marathon is a winter running event outside Grand Rapids, Michigan. Participants can choose from a marathon, half marathon, or a shorter moonlight race, all held on a certified course that's likely covered with snow. Known for its unique concept inspired by the movie "Groundhog Day," the event involves repeated loops of the course. It is organized with the help of the local running club, RunGR, which offers training programs for race participants. The event embraces winter conditions, and participants are advised to expect challenging weather.