It took 23-year-old Tom Dunn 92 days to complete the 4157 kilometre journey, known as Australia's Largest Triathlon and involving a cycle from Cape York to Sydney, a run from Sydney to Lakes Entrance, a swim to Sale and finally an Iron man to Wilsons Promontory that finished on Saturday.

It is Dunn's fourth extreme adventure after Kayaking the length of the Murray River, stand up paddle boarding down the Darling and hiking unguided to Mount Everest base camp.

Though he has form, the trip wasn't all smooth sailing for Mr Dunn. In fact, he said it nearly broke him.

“The swim leg was the toughest part," Mr Dunn said.

"I arrived after almost 70 days entirely alone, camping in parks or behind public toilets and at back of pubs. It was incredibly fatiguing to be searching for food and places to sleep along with the physical challenge of completing all those kilometres."

"The swim leg didn't go to plan, the weather was just a bit too unstable so I made the decision instead to jump in a kayak," he said.

Mr Dunn says he made a conscious choice to risk the dangerous swell. He could have left earlier, but he would have faced extreme heat in Queensland. The water was the “lesser of two evils”, to use his words.

Nonetheless, he says the loss of momentum took a heavy toll on his mental health, and he's learnt his limits and capabilities as a result of the trip. But he has also kept things in perspective.

"I'm only 23 years old and it won't be the last trip I do, so I guess by not pushing myself too hard this time it sets me up for that opportunity to go out and do another one later on.”

There is some more pressing unfinished business (not to mention some physio appointments) Mr Dunn needs to attend to first, however: As has been the case on previous trips, the 23-year-old's used the occasion to raise money for a good cause.

This time he chose Melbourne Indigenous Training School, a boarding house for Aboriginal students in Richmond.

“I work as a surf instructor down on the Coast,” Mr Dunn explained.

“I had a class with the kids just after I had the idea for this north to south trip, and in the space of 10 minutes some of the kids who'd never seen the ocean before were much better surfers than I'll ever be.

“They get the kids coming down from the Top End, and they spend a year at the MITS boarding house before getting a scholarship to some of the better schools in Melbourne.”

As of Monday, Mr Dunn had raised just under $3500 of a total $30,000 target, which is enough to put an extra student through MITS for one year.

“I’m actually quite happy with that, because throughout the journey I was very focused on surviving each day, so now the trip’s done I’m looking forward to going and doing some presentations, and hopefully promoting the fundraising side of things a little bit more.”