The 69-year-old from Townsville wore them out working on small navy ships back when limbs, rather than rubberised floors and spring-loaded seats, bore the brunt of the sea’s constant pounding.

Yet when his wife Davina suggested they undertake a gruelling 780km pilgrimage on foot from the French border all the way to Spain’s northwestern corner, Chad agreed to “plod along”.

They set off last September and walked almost non-stop for 35 days, covering up to 30km a day.

It gave his knee hell.

“We were in bars and all sorts of places bludging ice and plastic bags and things,” Chad says. “The worst was going downhill. I’d wake up at three in the morning and think: what am I doing here? I just had to grit my teeth and keep going.”

In January, after returning home, Chad’s doctor delivered bad news: the walk had done such damage that he’d need a partial knee replacement.

Yet, like so many before him, Chad remains captivated by this punishing adventure that briefly robbed him of his mobility.

Pilgrims have trekked Spain’s ancient Camino de Santiago since medieval times, but the route has only recently grown popular with Australians.

The number of Aussies completing the Camino more than doubled in the past two years, to 3098 according to official figures, though it is likely that far more attempt it.

They hike in pouring rain and baking sun, carrying their possessions on their backs and battling blisters, shin splints and knee injuries, sharing cheap 20-bed dorm rooms with dozens of other stinking, snoring and sweat-soaked strangers each night.

“The experience makes you a bit more humble,” Chad says. “Millions have done it and at the end, you can’t help but be moved.”

Many are drawn by the legend of martyred apostle St James the Great and the belief that, sometime after his death in the year 44, his remains were brought by boat from Jerusalem to Galicia in northwest Spain and buried beneath the city of Santiago de Compostela. For more than a thousand years, pilgrims have set off from cities and towns all over Europe on a grand journey of homage to James, the patron saint of Spain.

Today, the Camino Frances route is most popular, snaking from the southern French city of St Jean Pied de Port over the Pyrenees, then tracking for days across Spain’s flat and shadeless northern Meseta, or plateau, before entering the lush pastures of Galicia.

All roads lead to Santiago de Compostela’s towering Romanesque cathedral, the saint’s final burial place, where each day a special service is held to honour those who complete The Way of St James.

Naturally, then, the act of placing one aching foot after another for hours on end, day after day, is for some a way to find religious or spiritual enlightenment.

Such as Neil Millar and his partner Sarah Bachelard, both Anglican priests in Canberra, who were forced to resign in 2010 for falling in love. Millar was married and, though he had separated from his wife before pursuing his love for Bachelard, says he was “disappeared” after telling church elders about the situation.

“I found I was walking to work, and I just felt like I wanted to keep walking and walking and walking,” Millar, 56, says.

“There was this sense of just wanting to keep on a journey, on an adventure, walking towards something.”

In 2013, the couple walked the Camino to work through their anger and assess how they could continue serving God. In a way, the pain of their bruised feet, inflamed tendons and throbbing knees assuaged the mental anguish of being ostracised by their church community.

“It felt to me like a way of physically enacting the transition we’d been going through on all these different levels,” says Bachelard, 48.

“It almost felt like it could be a bridge we could actually cross, between where we were and the next phase of our lives.”

Almost 90 per cent of the 215,880 people on El Camino last year walked for religious or “religious and other” reasons, according to official statistics.

However, that figure is distorted because many list themselves as such in order to receive the pilgrim’s official certificate of accomplishment, or compostela. In fact, a huge number of agnostic, atheist or religiously indifferent folk find themselves trudging The Way of St James, myself included.

Last October a friend and I, both Queenslanders, eagerly set off at dawn from the small city of Sarria, aiming to cover the final 115km of the Camino Frances over six days, a popular choice for those without a whole month to spare.

We were woefully unprepared. The landscape of this top western corner of Spain is lush and green, all towering mountains, dense forests and rolling fields dotted with dairy cows — a far cry from the sun-soaked and dusty south I am accustomed to. It rained almost every day, with that kind of slow and steady persistence that seeps through waterproof clothing and leaves every inch of one’s self and belongings thoroughly soaked.

Bedraggled and sodden, our sneakers sloshing with water, we kept walking, following yellow arrows roughly painted on trees, signs and crumbling houses.

Each afternoon we traipsed wearily into a small hostel or albergue and handed over our official pilgrim passport to be stamped, authenticating our day’s journey and granting access to a rudimentary bed within a shared dormitory at just €10 ($A15) a night.

My unaccustomed left knee objected to the hours of walking and soon I found it difficult to stand by the end of the day.

One night, as we rested in one of those huge shared dorms, a middle-aged woman from Western Australia, busily tending enormous blisters that covered the entire sole of her foot, handed me a knee brace.

“I brought three thinking my knees would give out but it’s my ankle that’s the problem,” she told me, lifting her track pants to reveal an angry deep purple bruise circling her lower calf and heel.

She had decided to attempt the Camino after spotting a photo in a travel book, deeming herself physically fit for the challenge after successfully walking the 15km from her house into town and back.

Plenty are spurred into action by books and television shows, and especially the 2010 Hollywood film The Way, which depicted El Camino de Santiago as a life-changing journey of self-discovery. Brisbane barrister Kim Forrester, who walked late last year with her husband Julian after watching The Way, says her Camino was meditative, a chance to momentarily pause the busyness of life.

“I found the walking to be physically very difficult but it was a good opportunity to centre yourself because there’s nothing complicated going on,” Forrester, 59, says.

“You’re just walking, stopping for coffee, stopping for lunch, stopping to sleep, then getting up and walking again. It definitely was life-changing for me. I thought very seriously about what I’d been doing for the past 58 years and what was going to be important to me for the next, hopefully, several decades.”

Walter van Praag from Tasmania walked to stay alive.

At 49, van Praag is one of the oldest people in the world with cystic fibrosis, an incurable genetic disease that blocks the lungs and digestive system with thick mucus that breeds infection. Most sufferers do not live beyond 40.

“For me, it’s dying or exercising,” van Praag explains over the phone, puffing a little as he kayaks along the Mersey River near his home in Devonport during his daily hour of aerobic exercise.

“Cystic fibrosis affects your whole body, but the thing that kills us is lung infections. The only way to keep them going is lots of medicine and lots of exercise.”

In Spain, van Praag spent an hour every morning and night plugged into a nebuliser, coughing and spluttering as he gently inhaled his medication.

“You get used to strangers looking and you can tell they’re thinking: why are you out in public spreading disease? Why aren’t you home in bed if you’re really sick?” says South Australian Karina Deans, from Adelaide, who walked with van Praag last September.

“But it’s not contagious and it’s a lifelong condition. We were very conscious of letting everyone know around us why he was doing it. Most people were pretty considerate.”

Van Praag raised more than $10,000 for cystic fibrosis research during his Camino, but says he was humbled by other pilgrims’ stories.

“I saw people, 60-year-olds and older who were overweight, who’d had bypass operations, people with cancer who’d given up on treatment and decided to walk. At times I was almost embarrassed to say I was doing it because I’ve got cystic fibrosis.”

As the long Camino days wear on, camaraderie builds among the pilgrim community.

Each night you tend to bump into the same people, gradually piece together their stories and come to understand why they, too, have been drawn to this strange and difficult walk.

For all its physical challenges, walking the Camino is often more taxing mentally.

Long hours can pass in silence save for the crunching of your boots on gravel, and it is difficult to avoid contemplating your own life and choices. In this way the journey is somehow spiritual, even for those walking without religion.

“Buen Camino!” we call out to one another in passing as a greeting, an exchange of well wishes and an acknowledgment that we are all on this demanding journey together.

Some pilgrims, on finally reaching the grand cathedral of Santiago de Compostela, choose to continue walking even further west, another 90-odd kilometres to a rocky peninsula jutting into the Atlantic, which marks Spain’s westernmost point.

It’s known as Cape Finisterre, a Latin-derived name meaning “the End of the World”, and for many Australians coming from the opposite side of the planet, this feels true.

Out there at the end of the world, van Praag and his mates stripped and ran, totally free, into the ocean.

Millar and Bachelard hurled away small stones they had carried all the way from Australia, and with them a small piece of themselves they no longer needed.

“I had a lot of resentment to deal with and quite often I’d grab my little rock in my pocket and just try to channel the resentment into that rock because I was going to chuck it away at the End of the World,” Millar says.

“It was a symbol of getting to the end of the journey and going the whole distance. That was very meaningful and very powerful.”

Symbolism means a lot on this journey, which captures the imagination of people from all walks of life, especially those aged between 30 and 60. I was enticed by the idea of a walking meditation, that simply concentrating on where next to place my feet could somehow become a gateway to mental or spiritual enlightenment. Instead, I felt wholly grounded, constantly focusing on my physical discomfort and wishing for the end.

Yet now I find myself inexplicably drawn back to attempt the entire walk, for reasons that remain unclear.

At the conclusion of my own short Camino last year, as I stood before Santiago de Compostela’s cathedral, I bumped into Sue Stephens, 59, from Brisbane.

She and her husband Stefan had completed their 36-day journey the day before.

She was still visibly moved and even a little emotional about the experience, proud and perhaps subtly changed after following the same footsteps trudged by thousands of devotees over hundreds of years.

Later, she sent me a quote she’d noticed scrawled on the back of a billboard right at the

end of her walk. It was a song lyric by American musician Tom Petty: “Some things are over, some things go on / Part of me you carry, and part of me is gone.”