Its origins may stem from Ancient Greece, but the marathon run is still a distance that captivates and inspires athletes in the 21st century.
It's one of endurance sport's ultimate challenges and it's a distance not to be sniffed at: some 26.2 miles/42.2km where smart pacing is paramount, a nutrition strategy is mandatory and serious pre-event training is performed to avoid bonking at the dreaded 18-22 mile segment, often named 'The Wall'. But don't let us put you off; finish one and you'll remember it forever (and don't feel shame about bragging about it a bit, too).
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While marathon distances are largely standardised, the course elevations, underfoot terrain and weather conditions are not. Trail marathons, mountain marathons, fell marathons, road and trail combos and more all fill the marathon calendar worldwide. But which is the toughest? Here's our pick of UK and international marathons for you to be inspired and awed by, and perhaps even enter. Just don't forget the blister plasters...
Toughest marathons in the UK
Endurancelife Exmoor, Devon
Martinhoe, Exmoor; 10 May 2025
Endurancelife have been offering hugely testing coastal trail runs around the UK for years, but this marathon-length brute in Exmoor has long been seen as their toughest challenge.
Exmoor is an underrated and hilly devil: a land of towering sea cliffs, rugged moors and wooded combes, all of which feature on this 26.7-mile Exmoor beast.
Starting near Martinhoe in the quieter western area of one of England’s least visited and smallest national parks, the route includes stretches of the South West Coast Path at its most vertiginous in Countisbury and the Valley of the Rocks, as well as deep inland valleys. And all on an unforgiving underfoot terrain of rocks, grass and forest trails. The mighty elevation gain of 1,850m ensures a long day out at both ends of the field, with the winners coming home in around four hours and the final athletes close to the eight-hour mark. Don’t forget your blister patches….
If you want a taster before you romp home in the marathon next season, Endurancelife also offer a 6.3-mile (10km) option in Exmoor. Admittedly, with 451m of climbing, it’s still a brute where most of the field will take well over an hour to finish, but those Bristol Channel views should soften the pain somewhat.
Xterra Snowdonia Trail Marathon Eryri, North Wales
Llanberis, Wales; 12 July 2025
With a mighty 1,685 metres of elevation gain over its 27.3-mile route, this Eryri/Snowdonia-set corker jostles with Endurancelife Exmoor as the toughest trail marathon in the UK. The route circumnavigates and eventually climbs Wales' highest peak of Yr Wyddfa (Snowdon) before the leg-shaking descent back into Llanberis for one of marathon racing’s most welcome finish lines. And if that doesn’t sound tough enough for you, Always Aim High also organise the Slateman Ultra Triathlon in June, with a 2.4-mile swim and 112-mile bike before the marathon run.
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Eden Marathon, Cornwall
The Eden Project, St Austell, Cornwall; 19 October 2025
I ‘raced’ Cornwall’s Eden Marathon in 2023 and didn’t check the total elevation gain… until after I’d entered. Big mistake, as the mighty 1,000m of climbing over the 26.2-mile (42.2km) course puts at the top end of the UK’s major marathons and left me a shuffling shell of a man by the 20-mile mark – the half-marathon option would’ve been a wiser choice.
It was worth the golf ball-sized blisters, though, with the relentlessly rolling route taking in Cornish clay country, an epic climb to Helman Tor and the Eden Project’s famous biodomes at the finale (your supporters also get free Eden entry on the day).
The multi-terrain course largely takes place on country lanes and trails – I’d advise road shoes with decent grip or less aggressive trail shoes if the weather has been largely dry before the race. And did I mention that you get a free Cornish pasty and a can of Doom Bar at the finish? I’ll see you there in October.
Langdale Marathon, Lake District
Langdale, Lake District, Cumbria; 13 Sept 2025
This Lake District race is regularly labelled as the UK’s toughest road-based marathon due to its hilly course with 1,036m of elevation gain thanks to its double ascent of Blea Tarn. There’s also the high Did Not Finish (DNF) rate, with a study from New Balance revealing a 15% rate in 2022.
The world’s toughest marathons
The UK might offer some of the most consistently hilly terrain for runners, but the toughest worldwide contenders also throw high altitude and extreme weather conditions into the marathon mix. The Inca Trail Marathon in Peru takes runners back in time to a 500-year-old hand-laid cobbled path. Some 10,400 ft of elevation gain and four major mountain peaks stand in the hardy entrants’ way, with many taking up to 16 hours to complete the formidable challenge.
The Pikes Peak Marathon in California is the oldest continually held marathon in the USA and takes place on a mix of rocky, narrow and winding gravel tracks. Many runners take 8-10 hours to complete the marathon, slowed further by the brutal 2,382m of elevation gain.
With a highest point of 4,206m, the Kilimanjaro Marathon in Tanzania, Africa, is the highest organised marathon in the world and witnesses finishing times run up to 20 hours. Temperatures can drop below freezing at night, but there’s no cut-off for finishing.
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