Some of the best adventure athletes have lined up alongside Air Force pilots and former rugby stars at the start line for this year's Godzone race in Te Anau.
It's a gruelling challenge that will see teams traverse remote Fiordland wilderness over the next week.
The field of 400 athletes - racing in teams of four people - is the largest ever in the seven years of the South Island adventure race.
Five time adventure racing World Champion Nathan Fa'avae has returned after a two year absence, thanks to prompting from his wife Jodie.
"In April last year said she wanted to do Godzone", Fa'avaue says.
"And initially I said, Well that's great, I'd support you to go and do it. And she said to me, no, no, the catch is that if I'm doing it, you're doing it as well."
Godzone has a reputation as one of the world's pinnacle adventure races, and that's helped attract a strong international field.
One visiting team from the UK features three military pilots and an engineer, racing as Team RAF to celebrate the hundredth anniversary of the Royal Air Force.
"We've raced in previous races, we started in triathlon and liked the adventure racing", Team RAF Pilot Jamie Buckle says.
"And there's quite a few crossovers from some of the military training we've done. Some of the logistics, just some of the resilience you need. So it was kind of a natural lead-on."
Teams will race nonstop for the next week - with little to no sleep - navigating their way around the 550 kilometre course in Fiordland.
Packrafting is a new discipline for this year's race, with competitors also challenged with the likes of mountain biking, hiking, and kayaking.
Former All Blacks captain Richie McCaw has again teamed up with Red Bull Defiance teammate and veteran multisporter Bob McLachlan.
"There's a lot of water paddling, which Bob's pretty strong at", McCaw says.
"So having him here to guide is around will be damn good."
Athletes have been training for months.
Antarctica NZ scientist Fiona Shanhun even kept up her regime while working down on the ice.
"Yeah I had a month in Antarctica last year", she says.
"It was a bit chilly down there, quite a contrast to what we've got here today."
But conditions are set to get a lot tougher over the next few days.
Teams will spread out as they battle their own way around the remote course using just a compass and maps for navigation.