Climbing a freezing cold mountain is already hard enough work. But in briefs? Nope.

It's too late for Sydney teacher Ben Anderson and four friends. They conquered Australia's highest mountain, Mount Kosciuszko, while wearing very little at all back in early-July. And they lived to tell the tale.

The group were inspired by the antics of Wim Hof, a Dutch man nicknamed "The Iceman" due to his ability to withstand extreme cold, holding a number of world records for different feats.

"The idea came about last year, [my friend] Blake and I were discussing a podcast on Wim Hof," Anderson told Mashable Australia.

"We thought you know what, let's see if we can do that. So in November last year, we thought let's try and make it up Kosciusko in our swimmers in the middle of winter. And so we started training."

While it was difficult to train for the winter cold during the blaring heat of summer, the group prepared by taking ice baths, cold showers and going for swims in the middle of the night when temperatures were at their minimum.

"It's all about getting the mind and body familiar with what it's like to be cold. That's how you'll survive really," Anderson laughed.

The 13 kilometre (eight mile) trek to the summit of the mountain (and back) took four hours, with 3.5 of those hours done in swimwear. But they nearly didn't make it up. The group went up on the last day of their allotted four-day window, when the weather was finally good enough to climb.

"The weather is highly unpredictable, and it's not like we were going to go up in a blizzard. So we had to select the best day out of four days, and the Friday turned out to be the best day," Anderson said.

Image: kossie in cossies

By "best day," Anderson means chilly temperatures of minus four degrees Celsius (39.2 degrees Fahrenheit) at the summit, with winds ranging from 25 to 30 kilometres (15 to 18 miles) an hour. Despite the confronting weather, it was an experience that they relished.

"It was just an absolutely exhilarating experience. We trained and prepared ourselves very, very well so that we were able to do the climb quite easily," he said. "Other people might not believe that, well, most people don't actually — they're still wondering how the hell did you do that?"

The group did exercises along their trek to help regulate their body temperature, as inspired by Wim Hof. Despite the relative ease in getting up the mountain and the beautiful surrounds of Mount Kosciusko, Anderson isn't rushing to do it all in his swimwear all over again.

"I doubt whether there will be a similar sort of experience [again]. It was a really good physiological challenge, and sparked something for most of us to see what our bodies are capable of," he said.

It wasn't just for the thrill of it though. The group is also raising funds for Australian depression and anxiety charity, beyondblue, while also trying to show people what can be done with a bit of persistence and resilience.

If it's getting your pants off and freezing on an icy mountain for a good cause, so be it.