CHAMONIX-MONT-BLANC, France — There is a specific sound a mountain town makes during a trail running festival, and Chamonix is making it this week: the early-morning clatter of poles on cobblestones, the hiss of espresso machines feeding runners who will spend the day above 2,000 metres, and the low constant hum of a valley that has organised itself, for four days, entirely around the act of running up and down its own walls.
The Marathon du Mont-Blanc has begun. It is not a single race but a festival of them — five distances across four days, from the 10K to the 90K flagship, plus the youth Mini-Cross that puts the next generation of Chamonix runners on the same start line their parents use. The town centre's Place du Mont-Blanc is the hub: start line, finish line, expo, and the gathering point for a crowd that treats trail running the way other places treat football.
Where This Happens
Chamonix sits at 1,035 metres at the foot of Mont Blanc — at 4,808 metres, the highest summit in the Alps and the mountain that gives the valley its gravity. The town is hemmed between two ranges: the Mont Blanc massif to the south, with its glaciers and the Aiguille du Midi cable car climbing to 3,842 metres, and the Aiguilles Rouges to the north, whose balcony trails give the Marathon du Mont-Blanc its defining views.
This is not incidental scenery. The festival's routes are built along the high balconies of both sides of the valley — the trails that traverse at altitude with the full massif in view. When runners reach the high points of the 90K or the marathon, they are looking directly across at the Mont Blanc glaciers: the Mer de Glace, the Bossons, the séracs hanging off the Dôme du Goûter. The course is designed to put runners in front of that view at the moments they are working hardest.
The 90K: The Flagship
The 90-kilometre race is the festival's centrepiece and one of the most respected single-day mountain ultras in the Alps. It covers roughly 6,300 metres of positive elevation gain over a route that strings together the valley's high balconies — climbing out of Chamonix, traversing the Aiguilles Rouges side, dropping to Vallorcine near the Swiss border, and working back along the Posettes and Tré-le-Champ ridgelines before the final descent to town.
It is a course that rewards experience over raw speed. The climbs are long and sustained; the descents are technical alpine single track; the altitude stays high for hours at a stretch. The 90K field carries a concentration of skyrunning and UTMB-circuit athletes who use Chamonix in late June as a marker of form — the valley is, after all, where UTMB itself finishes in late August, and a strong Marathon du Mont-Blanc 90K is a statement about the season ahead.
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Join ZealZagFollow us on InstagramThe Marathon: Sunday's Main Event
The race the festival is named for — the Marathon, 42 kilometres with roughly 2,500 metres of climbing — runs on Sunday and draws the largest competitive field. The route is a classic: out of Chamonix, a long sustained climb through the forest and onto the Aiguilles Rouges balcony, a high traverse with the massif in full view, and a finish at La Flégère at altitude before the descent.
The marathon is where the festival's elite skyrunning talent concentrates. The combination of distance, vertical, and altitude makes it a true mountain marathon rather than a road marathon run on trails — the winning times reflect terrain, not just fitness. The front of the field is genuinely world-class.
The KMV, the 23K, and the 10K
The vertical kilometre — the KMV — is the festival's purest test: a short, brutally steep race climbing 1,000 metres of altitude over minimal horizontal distance, won by athletes whose physiology is built for one thing only. The 23K and 10K give the festival its breadth, putting thousands of recreational runners on shortened versions of the same balcony trails the 90K and marathon use.
The Town This Week
Chamonix in late June is at the start of its summer season. The Aiguille du Midi cable car is running, the mountaineers are heading up the Mont Blanc routes, and the trail running festival sits on top of all of it. The Place du Mont-Blanc expo is busy from morning to night; the restaurants on Rue du Docteur Paccard are full of people carb-loading or recovering; the valley's campsites and hotels are at capacity.
By Sunday evening, when the last marathon finishers climb the final ramp to La Flégère and the 90K results have long settled, the festival will have moved tens of thousands of runners through one of the most concentrated mountain landscapes in Europe. Then the town exhales, and turns its attention to the bigger event two months away.
What to Watch
The 90K result is the headline — a late-June form check for the UTMB-circuit elite. The marathon's skyrunning front end produces the festival's fastest, most tactical racing. And the KMV, run in under 45 minutes by the best in the world, is the most concentrated suffering on the programme.
For the full guide to running the Chamonix trails yourself — the balcony routes, the lift system, gear, and where to base in the valley — see our companion Marathon du Mont-Blanc Race the Route guide. For the other major alpine ultra in full swing this week, our Lavaredo Ultra Trail opening day report covers the 120K race week in the Dolomites.
Programme and elevation data via montblancmarathon.net. Field coverage by ZealZag Team.