In the heart of Île-de-France, nestled within the lush forests of Val-d'Oise, lies an annual trail running spectacle that challenges even the most seasoned athletes. The Trail of the 40 Bumps invites runners to venture into a winter wonderland in December, where elevation gains and scenic beauty await around every corner. The centerpiece event is the "Monster," stretching over two days with a grueling distance of 120 kilometers. This course features an impressive ascent of 4,900 meters D+, making it one of the toughest trails in the region. As runners traverse through chestnut groves and oak forests under moonlit skies, they will encounter terrain that tests both physical endurance and mental fortitude. The "Monster" is a true test for those who have trained on lesser hills like Montmartre. For those seeking a more moderate challenge, the 75-kilometer "Beast" offers similar scenic beauty but with an ascent of just 1,900 meters D+. This course still demands significant effort and resilience yet remains accessible to runners looking for a substantial day out in nature. Both events start near Saint-Leu-la-Forêt, where the forest landscapes provide a serene backdrop. On Sunday, shorter distances cater to all levels: 45 kilometers through historic trails, 20 kilometers offering glimpses of charming villages like Taverny and Saint-Prix, and a more manageable 10-kilometer route for those looking for an introduction. Each course winds its way through dense forests, past quaint towns, and alongside picturesque rivers. Post-race activities abound in the Val-d'Oise region. History enthusiasts will find much to explore at landmarks such as Chantilly Castle to the north or Écouen Castle with their extensive gardens perfect for a post-run stroll. For art lovers, Auvers-sur-Oise offers an immersive experience where one can trace Van Gogh's final days and artistic inspirations. The village of Roche-Guyon adds charm with its medieval ambiance, recognized as one of the most beautiful villages in France. Its serene setting provides runners a tranquil spot to unwind after their efforts on the trails. In December, join thousands at Saint-Leu-la-Forêt for an unforgettable trail running experience that combines breathtaking scenery and challenging terrain, making it the perfect conclusion to your year's training regimen.
Races Offered
Trail 120 km
Dec 05, 2026
straighten
Distance —
120K
terrain
Type —
Running
timer
16:30
sell
€110.00
Trail 75 km
Dec 05, 2026
straighten
Distance —
75K
terrain
Type —
Running
timer
16:30
sell
€80.00
Trail 45 km
Dec 06, 2026
straighten
Distance —
45K
terrain
Type —
Running
timer
08:30
sell
€50.00
Trail 20 km
Dec 06, 2026
straighten
Distance —
20K
terrain
Type —
Running
timer
10:00
sell
€30.00
Trail 10 km
Dec 06, 2026
straighten
Distance —
10K
terrain
Type —
Running
timer
14:00
sell
€20.00
Weather History
These values represent the 3-year monthly averages for December in Saint-Leu-la-Forêt.
thermostatTemperature
4.2° / 8.8°
wb_sunnyFeels like
0.3° / 5.4°
light_mode
Avg sunshine hours
2h 47m
water_drop
Avg rainfall
1.7 mm
ac_unit
Avg snowfall
—
air
Avg wind speed
13.5 km/h (Gentle breeze)
opacity
Sweat loss rate
Low
terrain
Course conditions
Firm and slightly soft
sunny
Max UV Index
Low (1.4)
humidity_mid
Humidity
88.0%
wb_twilight
Sunrise
09:37
nightlight
Sunset
17:55
About Saint-Leu-la-Forêt
Learn more about the host city, Saint-Leu-la-Forêt.
Saint-Leu-la-Forêt is a commune in the Val-d'Oise department, in the northwestern outer suburbs of Paris, France. It is located 19.9 km (12.4 mi) from the centre of Paris.
