I’ve been running uphill for over an hour, scaling this narrow mountain trail, when we pass through some trees. This must be the top, I’m thinking, hopefully, as we crest the pass. But alas, rising up on the other side are more hulking mountains and snaking up through the middle of them, like a line of ants, are the tiny dots of the runners ahead of us.

“Putain,” swears the French runner behind me. I know exactly how he feels. The 170km Ultra Trail du Mont Blanc is the most famous trail race in the world. In the fast-growing sport of Mountain Ultra Trail (MUT) running, it’s the big one, the sport’s Super Bowl. For a week at the end of August each year, the town of Chamonix in the French Alps is completely taken over by ultra runners and their supporters. Any unsuspecting visitors arriving in the area would be left baffled by this strange world of short shorts and little backpacks and super-fit people that they’d wandered into.

During UTMB week – which acts as the climax of the brand new UTMB World Series – about 10,000 runners compete across seven different races of varying lengths. I’m here to run the 100km CCC race, which starts in Courmayeur in Italy and follows a route around Mont Blanc, scaling more than 6,000m of ascent along the way, passing through Switzerland, before finishing in Chamonix.

Why would anyone want to run so far? It’s a good question. On one level, taking part in these races is an adventure into the wild. By traversing such great distances on foot, you get to explore some of the most remote corners of these incredible mountains. Sure, you spend a lot of time looking down at your feet, but every time you look up, the landscape takes your breath away.

But it is also a race. Despite my intention to primarily run to enjoy the experience, once we get going I find myself pushing hard and I finish in under 20 hours, an arbitrary goal I set myself before the start. You can choose to go slower, of course, but it doesn’t really make things any easier, since it just means you’re out there running for longer. So I decide to embrace the inherent competitiveness of the event and get my skates on. I can then spend the rest of the weekend relaxing and soaking up the unique atmosphere of Chamonix during UTMB week.

It’s handy that my hotel, La Folie Douce, is so close to the finish, so that after finally making it to Chamonix in the middle of the night, I can hobble back to a hot shower and a blissfully comfy bed. The next morning I spend a heavenly few hours stretched out by the hotel’s outdoor pool with stunning views across the mountains that look a little unreal in the morning sunlight, like a huge Athena poster backdrop.

Chamonix also has an abundance of great places to eat – an essential part of the post-race recovery process – from the fine seasonal French cuisine at the Mont Blanc Hotel, the oldest, most elegant hotel in town, to the hearty Soul Bowls and vegan burgers at the Bighorn Bistro (a favourite haunt of the big-eating elite ultra runners).

Once I feel recovered, I head back into town to sit outside a café and cheer the last UTMB runners home, each one creating a wave of noise from the crowds as they pass. For more than 100 miles and for up to 48 hours, they’ve been running up and down mountains, without sleep, and the effort is etched on their faces. Having done a race myself, I feel a connection to each runner that passes, and each time it brings a tear to my eye to see them so close to finishing their epic journey.

For more details on UTMB Mont Blanc, go to utmbmontblanc.com. La Folie Douce has rooms from £90 per night (lafoliedoucehotels.com)

Running highs: Other mountain trail events to test yourself on

To qualify for the UTMB races in Chamonix, you must compete in at least one of the 25 UTMB World Series events, where you can collect ‘running stones’ for the UTMB race lottery. Entries for the lottery open in December. Here are five of the best UTMB World Series events to consider.

Lavaredo Ultra Trail, Italy The serene rocky monoliths of the Dolomites play host each June to this long-established race on the European mountain running calendar. Setting off late at night from the town of Cortina d’Ampezzo – host city of the 1956 Winter Olympics – the race is brilliantly supported, with large crowds lining the streets to cheer you on your way. Best of all, being in Italy, you get to feast on endless pizza after finishing the race (lavaredo.utmb.world).

Speedgoat Mountain Races, USA Held in July on the slopes of one of the biggest ski resorts in the States, Snowbird in Utah, the Speedgoat 50k takes runners up gruelling climbs, across tricky, rocky terrain and through the breathtaking landscape of Utah’s Wasatch mountains. With the entire course situated above 2,300m, this is one of the toughest mountain races in the US (speedgoat.utmb.world).

Ultra Trail Snowdonia (UTS), Wales The only UK race in the UTMB World Series, the UTS follows challenging trails and traverses hairy ridges, summiting the most notable peaks in the north of the Snowdonia national park. Although the series of races – over 50km, 100km and 165km – take place in July, good weather is, of course, far from guaranteed (snowdonia.utmb.world).

Puerto Vallarta, México After crossing the Sierra Madre mountains, this race takes runners down through forests and agave plantations, into the jungle and then finally along the beach in the beautiful bay of Puerto Vallarta on Mexico’s Pacific coast. Taking place for the first time in October 2022, this new event’s longest race is 100 miles, while there are also shorter options of 100km, 50km and 20km (puerto-vallarta.utmb.world).

Doi Inthanon, Thailand This race takes place in December around the highest mountain in Thailand, Doi Inthanon, in the foothills of the Himalayas. The Doi Inthanon national park is famous for its waterfalls, remote villages and its sunsets – if you do the 170km race, you’ll run through at least one sunset and maybe even two, depending on how fast you are (inthanon.utmb.world).