Somewhere in the mountains around Kyoto live the marathon monks. Legend has it that the monks of Mount Hiei run 1,000 marathons in 1,000 days in their quest to reach enlightenment. Those who succeed become revered, as human Buddhas or living saints. It is rare that a monk embarks on the 1,000-day challenge, or kaihogyo, and even rarer that one completes it. In the last 130 years, only 46 men have managed it. I have come to Japan, hoping to meet one of them and to find out what they can teach a recreational runner about the path to spiritual wellbeing.

I can’t, however, just walk up the mountain and knock at his door. Visits are by invitation only. So at a private temple in northern Kyoto I, with my translator friend Max, meet a woman who knows one of the monks. She tells me that they run in straw sandals. She once met one on the last day of his challenge and expected to see his feet all swollen and sore. “But they were smooth and clean,” she says. “As though he had been floating over the ground.”

At the end of their quest, the monks enter a darkened room where they spend nine days without food, water or sleep. The idea is to bring the body as close as possible to death. Once they complete the challenge, they are given the title of Daigyoman Ajari, or Saintly Master of the Highest Practice. In imperial Japan, such monks were granted a special place at court, and were the only people allowed to wear shoes in the presence of the emperor. Today, those who complete the challenge become celebrities, television cameras transmitting the final stages of their journey live to the nation.

A priest at the temple tells me that the idea behind the constant movement is to exhaust the mind, the body, everything, until nothing is left. “When you are nothing, then something, pop, comes up to fill the space.”

He mimes a bubble popping.

This something, he tells me, is the vast consciousness that lies below the surface of our lives. A sense of oneness with the universe. I ask the woman about stories I’ve heard, too: that if they can’t complete the challenge, if they have to quit, they must kill themselves. She doesn’t know. This used to happen, yes, but now it is not clear. A lot of secrecy surrounds the marathon monks.

Months later, our invitation is finally granted. We collect the woman from the temple, along with a young man in a baggy jumper she introduces as her friend, then drive out of Kyoto. We’ve barely left the suburbs when we come to a stop outside some traditional buildings. This is where the running monk we’re going to meet lives. I had imagined more of a pilgrimage, hiking up some steep mountain path to a temple high in the clouds.

We get out of the car beside a garage filled with pots of paint and planks of wood. A beefy man in a tracksuit opens the door. This is the monk. We follow him across a small courtyard. “First he will do the ceremony,” the man in the jumper explains. He shows me how I can get my own prayer included in the ritual. Along one wall is a list of all the prayers you can make, from success in exams, or a job promotion, to simply your dreams coming true. It doesn’t seem particularly Buddhist, asking for the fulfilment of all these worldly desires, but I’m no expert. I opt for the prayer of good health for my family.

A marathon monk preparing for a run. Photograph: M YORKE

The man in the tracksuit returns, now wearing the white robes of a priest. He climbs up and settles himself cross-legged on the table, and starts chanting. It’s a continuous, rhythmic chant that sounds like a didgeridoo. It’s all in Japanese, of course, so to me it’s just deep, guttural sounds, until I hear my own name as he lays a stick on an ever-growing pile. Then suddenly it’s over. He stands up and says something matter-of-factly in Japanese, as though he has just come into the room to find us sitting there.

“So, what do you want to know?” he asks, settling down beside us.

I may be misreading him, but something about his demeanour suggests he is already impatient, as though he’s expecting me to ask him something stupid. I need to fire a deep, perceptive question at him, to win him over with my understanding of running and the path to spiritual enlightenment.

“I’m interested in why people run,” I begin. In answer, he starts explaining the whole process of the 1,000-day training. It’s not just about running, he says. Along the way, each day you need to stop at over 250 shrines and temples. The running is really just a way to get from one to the other. And it is not even running. Much of the time you are walking.

“But why?” I ask. “Why this 1,000-day challenge?”

He ponders for a moment.

“All humans are asking the question: ‘Why are we alive?’ he says. “The constant movement for 1,000 days gives you lots of time to think about this, to reflect on your life. It is a type of meditation through movement. That is why you shouldn’t go too fast. It is a time to meditate on life, on how you should live.”

“And when you did it,” I say, “did you find an answer to the question, why are we alive?” I may be pushing it here, but I’m waiting to hear about the sense of oneness with the universe he experienced. I want to know what reaching enlightenment actually feels like.

“There is not this one point of understanding where everything else stops and you’ve made it,” he says calmly. “Learning continues. Once you graduate from university, you don’t stop learning. The 1,000-day challenge is not an end point, the challenge is to continue, enjoying life and learning new things.”

These monks are purportedly some of the wisest, most spiritual men on earth, with insight gained through incredible feats of endurance. And yet here is a real-life Daigyoman Ajari telling me that running for 1,000 days was basically some good thinking time, and that really, afterwards, life went on as before.

“It’s like Lady Di,” he says. Lady Di? “Even though she was at the very top of English society, she found meaning in helping victims of landmines.”

Now he has really thrown me.

“What do people think?” he asks, leaning forward, watching me carefully. “Was it really an accident? I saw a television programme about it, and it seemed to suggest some dark forces were in action, that she didn’t die in a simple accident. What do you think?”

I shake my head: “I don’t know.” In some ways it’s a relief to know that even the highest Buddhists are sitting up in their temples in Mount Hiei watching television and gossiping about the death of Lady Diana. There is an idea, fostered by religion, that monks and priests are somehow different to us, free from the shackles of human desire. The reality is clearly different.

‘Sometimes I had slumps’ … Adharanand Finn with a marathon monk Photograph: Adharanand Finn

This can lead you in one of two directions. On one hand, you can despair. If the world’s spiritual guardians are sitting watching trashy TV, then surely we’re all doomed, a hopeless species trapped in a futile rush towards destruction. Or you can take solace from their everydayness. If the monks are like us, then it figures that we are like the monks. If they can gain a deeper understanding of life, yet still indulge their foibles, then perhaps we too can attain wisdom and fulfilment.

I ask him what he thinks. Are there similarities between what he found, and the experience of athletes and recreational runners? He says he saw a television programme about people training for the marathon and he was encouraged because he saw they often had slumps in their training.

“This was the same,” he says. “Sometimes I had slumps too, so it was good to see it wasn’t just me.”

Now he is finding solace in the trials of novice marathon runners. The 1,000-day challenge is such an extreme thing to do, and yet here is this man who has done it, and still suffers the same doubts, has the same questions as anyone else.

“Look,” he says, as though he is reading my thoughts. “Everyone needs to find something that suits them, that works with their body, with what they are doing in this life. I chose to undertake this challenge. But it is just one of many different paths to the same place.”

Sport is often seen in Japan as a way towards self-fulfilment, and the names of many of Japan’s most traditional sports, such as judo and kendo, end with the suffix -do, which actually means “the path” or “the way”. Running, too, can be a way to self-fulfilment. It has a purity, a power, a way of clearing the mind that few other activities possess. Sometimes it may seem unlikely, as we creak and struggle along, our legs heavy and tired, but then come those moments when we break through and our bodies begin to feel light, strong, at one with the earth.

But enlightenment, the monk says, isn’t a point where everything stops and you’ve made it, forever surrounded by a halo of bliss. It is something alive, something that pushes you on every day, whether you are a Daigyoman Ajari on Mount Hiei or a data-management assistant in an office in Hounslow. Something deep inside us wants to know that place, to find it again, to return to it. And for some of us, it means lacing up our shoes and heading out for another run.

This is an edited extract from Way of the Runner by Adharanand Finn, published on 2 April by Faber & Faber (£14.99). To order a copy for £11.99 with free UK P&P, call 0330 333 6846 or visit guardianbookshop.co.uk