Nearly 700 kilometres on foot through the snow, pulling a sled with everything needed to survive in temperatures as low as minus 45 degrees.
Not a normal choice of running race, but one Scott Thomson, of Wooragee in north-east Victoria, embraced.
He has returned from northern Canada after completing the Yukon Arctic Ultra, an annual ultra marathon described as the world's coldest and toughest.
Thomson, 37, began running ultra marathons when he was 30, challenging himself to bigger, longer, harder races.
"A number of years ago I was curious about what was the hardest footrace in the world," he said.
An online search threw up the Yukon Arctic Ultra, a continuous multi-stage race on foot, cross-country skies or mountain bike over a marathon, 100 miles (161 kilometres), 300 miles (483km) or 430 miles (nearly 700km).
"I found that whole environment fascinating, I mean it's so different to where we live," Thomson said.
"From when I was a kid, I'd sort of had a fascination with polar explorers, I'd always wanted to go to the South or North Pole."
A former public servant who is now studying horticulture, Thomson's research into the race stopped being merely academic.
"Could I do it?" he wondered. "Did I have what it would take to cope with those sort of distances and all the other associated challenges that go along with it?"
His partner Katrina Pawley supported his dream.
"I guess it took a while to actually believe, because of the scale of it, what it was," she said.
"It was so unique and extreme what he was doing."
To prepare for the ultra, Thomson put kilometres into his legs.
"I'd walk from my place to Bright which is 70km door to door and I'd do that in about 13 hours with a weighted backpack," he said.
There were hill repetitions at Mount Buffalo ("up and down that for hours on end") and shorter power walks of 30 to 40 kilometres, all while carrying a load.
Replicating the Yukon's weather conditions in Australia wasn't possible, so the athlete didn't try.
"Training in the Australian summer was ironically really good training," he said.
"Rather than being acclimatised to the cold, what you get from it is an ability to cope - you can't escape the heat.
"A key part of the race is that it is going to be hard, it is going to be very uncomfortable, it is going to be painful, but you have to find a way to cope with that and keep moving."
Adding to his motivation was the fact two years ago he had to pull out of the Yukon Arctic Ultra on day six with an injured ankle.
"That was probably one of the single hardest things I've ever done in my life," Thomson said.
Even before the injury, he had been struggling with fatigue.
"I found during that event some of my equipment didn't keep me warm as advertised," he said.
"I had about eight and a half hours' sleep over the five days. I made a lot of mistakes during that first go."
As difficult as that was for Thomson to endure, and for Ms Pawley to watch, the 2017 trauma played a significant role in last month's success.
Competitors in the 2019 Yukon Arctic Ultra set off on February 3 from Whitehorse, with the race to finish on February 16, even if some had not completed the course.
Although entirely self-supported, the athletes had a spot tracker and race guides on snowmobiles tried to reach each competitor at least every second day to check in on them and rescue any that couldn't continue.
Thomson opted for the longest distance, as did 39 others, most of whom also tackled it on foot.
Towing all his gear behind him in a sled weighing 25 to 30 kilograms, he'd settle into a sustainable pace and walk for up to 20 hours a day.
His rest was often sleeping a few hours next to the trail protected by equipment like a waterproof bivvy bag, foam mat, insulated airbed and winter sleeping bag.
Getting up into minus 30 degrees, he'd pack everything up, put on the harness and keep walking.
"You would just continually push on until you either had to sleep again the next night or you reached one of the checkpoints," Thomson said.
The checkpoints offered a meal and compulsory medical checks, with competitors scratched if they showed signs of frostbite.
Race stages ranged from 42km to 159km in distance, with the longest legs the last two for the 700km entrants.
Keeping out the cold was crucial, but nor could the athletes work up a sweat as the cooling effect and damp clothes would reduce body temperature quickly once the walker took a break, increasing the chances of hypothermia.
The risks are real - last year Italian competitor Roberto Zanda became disorientated, left his sled and suffered severe frostbite before he could be rescued.
According to later reports, his lower legs and right hand had to be amputated while doctors managed to save metacarpal bones in his left hand and reconstructed his thumb.
As well as the physical test, the extreme conditions produce a psychological effect.
"You spend so long alone and most of the race is done in darkness, the nights go for maybe 17 hours or so, they can really play on your mind and create doubt," Thomson said.
He felt he held up quite well overall, knowing his race was panning out much better than his previous attempt.
"I guess that confidence helped a lot," he said.
"It was still mentally very challenging, but as those negative emotions came up I was able to really knock them on the head straight away and keep going."
Ms Pawley said observing from the checkpoints was much easier this year and she felt confident her partner had done the necessary research and training.
"He has his systems down pat, he had his eating right, he could have just kept going," she said.
"I was just so excited that he had achieved his goal that he'd been training basically three years towards."
Eleven days, nine hours and 53 minutes after starting, Thomson crossed the finish line at Dawson City in fifth place overall, third male, and one of only 12 people to complete the ultra's maximum distance.
"I just felt really content actually, by the end you're sort of in a routine, so I could have kept going," he said.
"But I was very happy not to."
Thomson and Ms Pawley spent an extra week in the US on holiday but their adventure hadn't quite ended.
"He actually proposed the day after the race," Ms Pawley said with a smile.
Thomson returns to training next week, with future goals including the 100km Ultra-Trail Australia in May and maybe another overseas expedition in 2020.
But the Yukon event will be hard to top.
"One of the best things I've done, I think, just to be able to complete that," Thomson said.
"You wonder what else can you do if you're able to do that."