It was way too hot.
The Auckland endurance athlete is preparing for his first attempt at the 482km Yukon Arctic Ultra marathon, in February, that could be raced in temperatures below -50degC.
"The requirements for the race are that you have a sleeping bag rated down to -40. So when you get in here [a tent at the Snow Farm] at -15, you are just too hot.
"You are lying there cooking."
Charles said at very low temperatures organisers of the Yukon event did "get a little bit nervous," and would instantly disqualify any competitor with signs of frostbite.
"Your hands and feet, you can lose them in those sorts of temperatures."
The eight-day marathon follows in the footsteps of the sled dog teams taking part in the famous 1600km Yukon Quest race through Canada and Alaska.
Charles (44) had the choice of competing on cross-country skis, on a "fat bike" or walking, towing a 20-25kg sled with his provisions.
He chose walking and has spent months training in the Waitakere Ranges with a tyre.
"Pulling a tyre is a little bit harder than pulling a sled, because the sled tends to glide," Charles said.
He will tow his sled with poles rather than ropes so he has better control.
"Downhill it’s going to chase you.
"You don’t want it to take your feet out from underneath you."
Charles said each athlete had to be self-sufficient for two days, carrying a tent, sleeping bag, stove, food, water and an emergency beacon.
The event is held in midwinter and competitors spend much of the time racing in the dark.
Charles expected to cover about 60km in an 18 to 20-hour day of racing.
"That’s only 3km an hour, so it’s reasonably slow going."
He entered the race on the recommendation of another athlete while competing in the week-long race across the Gobi Desert.
He acted as a volunteer during February’s Yukon race and said the terrain was mostly undulating and forested.
The course also crosses frozen lakes.
He expected bears to be hibernating and the wolves to be heard but not seen, but would be on the lookout for charging caribou.
Charles expects to be the only New Zealander in the race.
