"Gruelling" was the first word that came to Jens Ambjerg-Peterson's mind after crossing the finish line with a time of 10 hours in one Australia's most testing adventure races.
Most tackle the 80-kilometre multi-sport challenge — which involves six different legs — as a team, while a handful take on the entire challenge alone.
On Sunday, 52-year-old Mr Ambjerg-Peterson was out to prove age is no barrier.
Two years ago, in his first attempt, he ended up taking himself to the emergency room with two badly injured wrists and a near case of delirium.
"Last year I came last. Last. I didn't do any training prior to it," he said.
This year though, with six weeks of training behind him, he hoped it was going to be a different story.
The Katherine Ultra Challenge starts at the crack of dawn, with dozens of swimmers navigating rocks in an open swim through the sandstone escarpment of Nitmiluk National Park.
The race involves a kayak, a trail run through the bush, a 40km road ride as the heat of the day increases, then an 18km rocky mountain bike trail … followed by another testing run to finish.
With teammates tagging each other into the next leg of the event, the race also tested competitors on their transition.
From humble beginnings in 1999, when just 20 racers crossed the finish line, the event now attracts hundreds of competitors and spectators.
Founder Jenny Anderson, who won the race in 2001 on account of there being no other female competitors, said the challenge used to be even tougher.
"The concept was 100 K in a day," she said.
"We were all new to it so there were a lot of people going off course, but they all survived in the end."
She said the Ultra Challenge was undoubtedly one of the only races of its kind in Australia.
"There wouldn't be many multi-endurance events that take in such beautiful country."
In previous years, the swim and canoe leg have been altered and moved after sightings of saltwater crocodiles in Katherine Gorge but this year had the all clear.
Katherine Multi Sport Club president Bronwyn Humphrys said the focus this year was on "making it a little bit less on the hardcore side and a little bit more on the enjoyable/competitive side".
"We didn't want to make it into an orienteering race where we had to get people to take a compass out with them," she said.
"We wanted them to either relax along the course.
"Or [for] those that are going that bit harder, to actually be able to compete rather than worry about which way they have to turn."
Sharon Campbell travelled from Tasmania and took on the four-kilometre canoe and eight kilometre trail run in her team.
She described the event as "hot".
"I loved the paddle, it was nice and cool and in the shade, but the run was really steep to start off with and then it plateaus.
"I was carrying a lot of water because I knew I was going to get really hot.
"I've just dumped it all over me to try cool down."
Dan Hewitt said the ultra-challenge had been a bucket list race for four years, and finally this year he was able to form a team.
"It's something really unique," he said.
"There are triathlons where you swim, ride, run, but nothing where you get to canoe.
"It was a tandem canoe today which made it more fun, mountain biking, trail running, there's nothing really that I know that's like it."
He said that even though he was a seasoned runner, the "tough climb" that starts the trail run was a killer.
"There are some very, very steep sections of it going up and down – but you can take it as easy or as hard as you like – you can really try pump out a quick time or you can slow down and enjoy the view a bit more," he said.
Ambitiously, he has plans to come back next year to tackle the event solo.
"This year I was thinking about doing the whole thing but I've only been doing triathlon stuff for a year or so, so next year it's a definite," he said.
The fastest teams started rolling past the finish line at noon, after their last teammate traversed the rocky and sandy 10km outback road run.
For Jens Ambjerg-Peterson, the six weeks of training paid off.
Crossing the finish to loud cheers from proud friends and family, as organisers packed up, and nearly everyone else had gone home, he said the toughest leg was the mountain bike ride, which crisscrosses the Southern Escarpment of Nitmiluk National Park.
"I had a few stacks, so I'm very sore in the hips, very very sore in the hips."
"Next year I'll jump on and be one of the volunteers."
