About 100 men and women are taking part in a gruelling series of races across the northern Yukon territory in Canada.
Facing temperatures as low as minus 40 degrees Celsius, snowstorms and immense tracts of wilderness, racers in the Yukon Arctic Ultra run distances ranging from a traditional marathon to a jaw dropping 690km run that takes at least 10 days.
Al Jazeera's Daniel Lak reports from northern Yukon.
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