Ecorun Frileuse 20 km is a timed trail race within the Frileuse military camp in Beynes, Yvelines, west of Paris. This nature race uses trails and paths, with a field limited to 500 participants and a morning start. This event is the longest option in the Ecorun Frileuse series, which also features 10 km and 5 km races.
The course consists of four laps of a 5 km loop, beginning and ending opposite hangar 213 within the camp. Participants will ascend 290 metres, enough to ensure the repeated loop is more than a flat tempo run. The location is a key feature: the Frileuse camp serves as a training ground for the French Army and the GIGN, meaning runners compete on terrain typically utilized by elite military and gendarmerie units. Organisers recommend the 20 km distance for experienced runners and advise entrants to bring a cap for sun protection.