Yukon, Canada - In Canada's northwestern territory of the Yukon, an extraordinary event has been taking place since 2003 - the Yukon Arctic Ultra.
It's a marathon on bike, foot and cross country ski that runs through the frozen wilderness from Whitehorse to Dawson City.
Participants can opt to run a traditional 26.2 mile marathon (42km), 100 mile (161km), 300 mile (483km) or - every second year - the grueling 430 mile race (692km).
They carry their own supplies - food and clothes - on bike or a sled they've got strapped to their waist and drag along.
There are a handful of checkpoints along the route where they can sleep indoors and get a hot meal and hot water but several nights have to be spent outdoors.
This February, dozens of athletes from all over the world took part.
The extreme cold, with temperatures running as low as -50 Celsius, led to many dropouts early in the race.
One racer from Poland, Michael Kielbasinski, landed in hospital with severe frostbite to his hands and feet.
Others complained it was impossible to sleep in those extreme temperatures and the only way to stay warm was to keep moving, even in the dark.
The first person from the 692km race to cross the finish line in Dawson City this year was Italy's Enrico Ghidoni, who competed on his bike.
The 61-year-old completed the race in just over a week, despite issues with his bicycle.
He's familiar with the route - in 2009, he was the first person ever to win the event on foot, and in 2013, the first to complete the distance on skis.
When the first runner came across the following day, fellow Italian Hanno Heiss, he joked they'd have to make up a new category for Ghidoni.