Not only did it lead to Raynor’s bestselling memoir, The Salt Path, but Moth’s health improved, too.

Worried that Moth’s health was declining post-pandemic, they decided to do it again, but walk further. This time they walked the length of Britain, some 1,000 miles. Another bestseller, Landlines, followed, as did a significant improvement in Moth’s condition.

Raynor asked at the end of their walk: “Is 1,000 miles far enough to turn darkness into light? Can using a body in the way it was made to be used reverse symptoms that are thought to be irreversible?”

Professor Anthony Hannan, of the University of Melbourne’s Florey Institute of Neuroscience and Mental Health, in Australia, explains why walking is so good for us.

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Physical activity – including walking – has beneficial effects on every organ in our bodies, including our brains.

It increases blood flow to organs. It strengthens the immune system. It can affect the trillions of microbes in our gut that interact with every other organ in the body, including the brain.

He agrees that using a body the way it was made to be used is important.

“We are evolved to walk long distances, as hunter-gatherers,” he says, adding that as well as delaying disease, physical activity may help slow its progression.

What diseases? Lots, according to research – walking has the power to reduce the risk of developing cancer, for example.

The American Cancer Society encourages walking; studies indicate it could lower the risk for up to seven types of cancer. One study found that women who briskly walked more than 7.5 hours a week had a 6 per cent lower risk of breast cancer than those who walked just three.

Another study found that seven hours of brisk walking a week reduced the risk of colorectal cancer – the most common cancer in the West – by up to 40 per cent.

And, according to the American Heart Association, walking briskly for up to 30 minutes a day can prevent and control high blood pressure, reducing the risk of a stroke by up to 27 per cent.

There have been a number of studies that show that walking a brisk 10,000 steps a day lowers the risk of dementia and Alzheimer’s disease.

So given the convincing disease-preventing effects of walking, it makes sense that it might bear curative powers.

Neuroscientist Shane O’Mara, a professor of experimental brain research at Trinity College Dublin, in Ireland, and author of In Praise of Walking: The New Science of How We Walk And Why It’s Good For Us, calls it “the super power you didn’t know you had”.

As he points out, walking is good for our muscles and posture, helps to protect and repair organs, and can slow or turn back brain ageing.

“Walking enhances every aspect of our social, psychological and neural functioning,” he writes. “It is the simple, life-enhancing, health-building prescription we all need, one that we should take in regular doses, large and small, at a good pace, day in, day out, in nature and in our towns and cities. We need to make walking a natural, habitual part of our everyday lives.”

Little wonder walking has even been called a “miracle cure”.

Professor Henning Budde at MSH Medical School Hamburg, in Germany, has a special interest in exercise neuroscience. He explains why physical activity is so important for brain health.

“The hippocampus, a part of the brain important for memory, is also the part of the brain where neurogenesis – the process in which new neurons are formed – applies, and this is supported by physical activity,” he says.

“Physical activity also leads to a release of hormones and growth factors which are important to sustain and improve physical and physiological health.”

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Yoga therapist and hiking guide Gabi Baumgartner, who runs guided tour company Walk Hong Kong, also sees the power in movement.

“Moving our bodies keeps us healthy. We are made for movement,” she says. “Digestion, circulation, the health of joints and bones, our brain and our moods, are all stimulated simply by walking.”

She describes how spending three weeks in a quarantine hotel during the Covid-19 pandemic affected her.

“I thought I was prepared. I packed my painting kit, books and a yoga mat. Three days in and I was lost, lonely and unmotivated.

“I realised I needed movement and decided to walk 10,000 steps each day. I walked back and forth in my room for an hour every morning and an hour in the afternoon. I listened to podcasts to make it more interesting.”

She ramped it up with an additional 10-minute run. “I have never been a runner so this felt new and exhausting,” she says.

Moving changed everything. “Food tasted better, there was a feeling of accomplishment and I slept well at night. My motivation returned. I left the room after 21 days in a physically, mentally and spiritually healthy state.”

Raynor believes that her husband’s marked improvement in health after their long walks comes down to neuroplasticity, defined as the brain’s ability to form and reorganise synaptic messaging.

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It seems the answer to Winn’s question – is 1,000 miles far enough to turn darkness into light? – is a definite yes.