The Trail des 40 Bosses is a renowned trail running event held annually in the Montmorency Forest, offering races of 10 km, 20 km, 45 km, 75 km, and 120 km. Participants can enjoy the natural beauty of the forest while tackling challenging courses with significant elevation gains. The event includes a night race, adding an extra layer of excitement for participants. With a variety of distances, the event caters to both novice and experienced trail runners. The event is known for its scenic routes and the unique challenge of running through the forest's diverse landscapes.
Races
Race Date:
07 December, 2025
The Le Sprint 10 km is a trail running race held in the scenic region of Saint-Leu-la-Forêt, Val-d'Oise, France. Participants will experience a challenging course with an elevation gain of 400 meters, traversing through forested areas and natural landscapes.
Race Date:
07 December, 2025
La Classique 20 km is a popular trail running race held in the scenic forests and natural landscapes of Saint-Leu-la-Forêt, France. The race features a challenging course with an elevation gain of 900 meters.
Race Date:
06 December, 2025
La Nocturne 20 km is a night trail race held as part of the Trail des 40 Bosses in Saint-Leu-la-Forêt, France, offering runners a unique experience through the Montmorency Forest under the cover of darkness. The course covers approximately 20 km with ~900 m of elevation gain, combining technical forest trails and challenging climbs.
Race Date:
07 December, 2025
L’Historique 45 km is a challenging mid-distance trail race within the Trail des 40 Bosses event, held in the Montmorency Forest, France. The course covers approximately 45 km with ~2,100 m of elevation gain, featuring technical forest trails, steep climbs, and scenic natural terrain.
Race Date:
06 December, 2025
La Belle 75 km is a long-distance trail race held as part of the Trail des 40 Bosses in the Montmorency Forest, France. Covering approximately 75 km with ~3,300 m of elevation gain, it challenges runners with technical trails, steep climbs, and varied forest terrain.
Race Date:
06 December, 2025
Le Monstre 120 km is the flagship ultra-trail race of the Trail des 40 Bosses, taking place in the Montmorency Forest, France. Spanning approximately 120 km with ~5,500 m of elevation gain, it offers an extreme challenge of technical trails, steep climbs, and demanding natural terrain for experienced ultra-runners.
Weather based on historical averages.
FAQs
What is the Le Sprint 10km?
How long is the Le Sprint 10km?
Where does the Le Sprint 10km take place?
What is the elevation gain of the Le Sprint 10km?
How can I prepare for the Le Sprint 10km?
How do I choose the right training plan for the Le Sprint 10km?
The Le Sprint 10 km is a trail running race held in the scenic region of Saint-Leu-la-Forêt, Val-d'Oise, France. Participants will experience a challenging course with an elevation gain of 400 meters, traversing through forested areas and natural landscapes.
The Le Sprint 10km is 10km long.
The Le Sprint 10km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
The Le Sprint 10km elevation gain is 400 meters, which Runna classifies as a Flat race.
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the Le Sprint 10km?
The Le Sprint 10 km is a trail running race held in the scenic region of Saint-Leu-la-Forêt, Val-d'Oise, France. Participants will experience a challenging course with an elevation gain of 400 meters, traversing through forested areas and natural landscapes.
How long is the Le Sprint 10km?
The Le Sprint 10km is 10km long.
Where does the Le Sprint 10km take place?
The Le Sprint 10km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
What is the elevation gain of the Le Sprint 10km?
The Le Sprint 10km elevation gain is 400 meters, which Runna classifies as a Flat race.
How can I prepare for the Le Sprint 10km?
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
How do I choose the right training plan for the Le Sprint 10km?
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the La Classique 20km?
How long is the La Classique 20km?
Where does the La Classique 20km take place?
What is the elevation gain of the La Classique 20km?
How can I prepare for the La Classique 20km?
How do I choose the right training plan for the La Classique 20km?
La Classique 20 km is a popular trail running race held in the scenic forests and natural landscapes of Saint-Leu-la-Forêt, France. The race features a challenging course with an elevation gain of 900 meters.
The La Classique 20km is 20km long.
The La Classique 20km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
The La Classique 20km elevation gain is 900 meters, which Runna classifies as a Hilly race.
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the La Classique 20km?
La Classique 20 km is a popular trail running race held in the scenic forests and natural landscapes of Saint-Leu-la-Forêt, France. The race features a challenging course with an elevation gain of 900 meters.
How long is the La Classique 20km?
The La Classique 20km is 20km long.
Where does the La Classique 20km take place?
The La Classique 20km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
What is the elevation gain of the La Classique 20km?
The La Classique 20km elevation gain is 900 meters, which Runna classifies as a Hilly race.
How can I prepare for the La Classique 20km?
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
How do I choose the right training plan for the La Classique 20km?
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the La Nocturne 20km?
How long is the La Nocturne 20km?
Where does the La Nocturne 20km take place?
What is the elevation gain of the La Nocturne 20km?
How can I prepare for the La Nocturne 20km?
How do I choose the right training plan for the La Nocturne 20km?
La Nocturne 20 km is a night trail race held as part of the Trail des 40 Bosses in Saint-Leu-la-Forêt, France, offering runners a unique experience through the Montmorency Forest under the cover of darkness. The course covers approximately 20 km with ~900 m of elevation gain, combining technical forest trails and challenging climbs.
The La Nocturne 20km is 20km long.
The La Nocturne 20km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
The La Nocturne 20km elevation gain is 900 meters, which Runna classifies as a Hilly race.
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the La Nocturne 20km?
La Nocturne 20 km is a night trail race held as part of the Trail des 40 Bosses in Saint-Leu-la-Forêt, France, offering runners a unique experience through the Montmorency Forest under the cover of darkness. The course covers approximately 20 km with ~900 m of elevation gain, combining technical forest trails and challenging climbs.
How long is the La Nocturne 20km?
The La Nocturne 20km is 20km long.
Where does the La Nocturne 20km take place?
The La Nocturne 20km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
What is the elevation gain of the La Nocturne 20km?
The La Nocturne 20km elevation gain is 900 meters, which Runna classifies as a Hilly race.
How can I prepare for the La Nocturne 20km?
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
How do I choose the right training plan for the La Nocturne 20km?
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the L’Historique 45km?
How long is the L’Historique 45km?
Where does the L’Historique 45km take place?
What is the elevation gain of the L’Historique 45km?
How can I prepare for the L’Historique 45km?
How do I choose the right training plan for the L’Historique 45km?
L’Historique 45 km is a challenging mid-distance trail race within the Trail des 40 Bosses event, held in the Montmorency Forest, France. The course covers approximately 45 km with ~2,100 m of elevation gain, featuring technical forest trails, steep climbs, and scenic natural terrain.
The L’Historique 45km is 45km long.
The L’Historique 45km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
The L’Historique 45km elevation gain is 2100 meters, which Runna classifies as a Hilly race.
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the L’Historique 45km?
L’Historique 45 km is a challenging mid-distance trail race within the Trail des 40 Bosses event, held in the Montmorency Forest, France. The course covers approximately 45 km with ~2,100 m of elevation gain, featuring technical forest trails, steep climbs, and scenic natural terrain.
How long is the L’Historique 45km?
The L’Historique 45km is 45km long.
Where does the L’Historique 45km take place?
The L’Historique 45km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
What is the elevation gain of the L’Historique 45km?
The L’Historique 45km elevation gain is 2100 meters, which Runna classifies as a Hilly race.
How can I prepare for the L’Historique 45km?
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
How do I choose the right training plan for the L’Historique 45km?
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the La Belle 75km?
How long is the La Belle 75km?
Where does the La Belle 75km take place?
What is the elevation gain of the La Belle 75km?
How can I prepare for the La Belle 75km?
How do I choose the right training plan for the La Belle 75km?
La Belle 75 km is a long-distance trail race held as part of the Trail des 40 Bosses in the Montmorency Forest, France. Covering approximately 75 km with ~3,300 m of elevation gain, it challenges runners with technical trails, steep climbs, and varied forest terrain.
The La Belle 75km is 75km long.
The La Belle 75km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
The La Belle 75km elevation gain is 3300 meters, which Runna classifies as a Hilly race.
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the La Belle 75km?
La Belle 75 km is a long-distance trail race held as part of the Trail des 40 Bosses in the Montmorency Forest, France. Covering approximately 75 km with ~3,300 m of elevation gain, it challenges runners with technical trails, steep climbs, and varied forest terrain.
How long is the La Belle 75km?
The La Belle 75km is 75km long.
Where does the La Belle 75km take place?
The La Belle 75km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
What is the elevation gain of the La Belle 75km?
The La Belle 75km elevation gain is 3300 meters, which Runna classifies as a Hilly race.
How can I prepare for the La Belle 75km?
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
How do I choose the right training plan for the La Belle 75km?
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the Le Monstre 120km?
How long is the Le Monstre 120km?
Where does the Le Monstre 120km take place?
What is the elevation gain of the Le Monstre 120km?
How can I prepare for the Le Monstre 120km?
How do I choose the right training plan for the Le Monstre 120km?
Le Monstre 120 km is the flagship ultra-trail race of the Trail des 40 Bosses, taking place in the Montmorency Forest, France. Spanning approximately 120 km with ~5,500 m of elevation gain, it offers an extreme challenge of technical trails, steep climbs, and demanding natural terrain for experienced ultra-runners.
The Le Monstre 120km is 120km long.
The Le Monstre 120km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
The Le Monstre 120km elevation gain is 5500 meters, which Runna classifies as a Hilly race.
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
What is the Le Monstre 120km?
Le Monstre 120 km is the flagship ultra-trail race of the Trail des 40 Bosses, taking place in the Montmorency Forest, France. Spanning approximately 120 km with ~5,500 m of elevation gain, it offers an extreme challenge of technical trails, steep climbs, and demanding natural terrain for experienced ultra-runners.
How long is the Le Monstre 120km?
The Le Monstre 120km is 120km long.
Where does the Le Monstre 120km take place?
The Le Monstre 120km takes place in Saint-Leu-la-Forêt, Val-d'Oise, Île-de-France, France.
What is the elevation gain of the Le Monstre 120km?
The Le Monstre 120km elevation gain is 5500 meters, which Runna classifies as a Hilly race.
How can I prepare for the Le Monstre 120km?
The best way to train for the next race is to use a personalized training plan that takes into account your current running ability, schedule, and preferences.
This will help you steadily improve your running performance and get ready for the race without risking an injury.
Check out our training plans to find the best running program for your goals!
How do I choose the right training plan for the Le Monstre 120km?
Which plan you choose will depend on your experience, schedule, objectives, and the date of the race.
Runna offers personalized training plans for every runner and every goal: Whether this is your first, 10th or 100th race, we'll help you get the most out of your training and smash your goals.
Check out our training plans to find the best running program for your goals!
This event listing is for informational purposes only. Runna is not affiliated with, endorsed by, or sponsored by Trail des 40 Bosses or Les 40 Bosses association. All event details are based on publicly available information and are provided solely to help users discover running events. Runna does not use any official logos, images, or proprietary content from this event or its organiser. Any trademarks or names mentioned are used descriptively to identify the event in a factual manner. For the most accurate and up to date information (including to register or purchase an entry to the event), please visit the Trail des 40 Bosses website.
