Robert Louis Stevenson offers the very rare example of a great writer who excelled in nonfiction as much as fiction. Contemporary critics also puzzled over the character of his greatness. Would Stevenson, asked one in 1892, “take his definite and final place in English literature as a writer of essays or novels?”

Today, the answer to that question might seem obvious. Treasure Island, Kidnapped and Dr Jekyll and Mr Hyde remain imperishably popular – timeless and universal. At the same time, Stevenson’s travel writing, a small part of his nonfiction output, is as outstanding and influential as his fiction. What’s less often acknowledged is the fact that it was Stevenson’s poor health that drove him to travel abroad: he was always in search of relief for his chronic bronchial condition (possibly tuberculosis) and the frequent haemorrhages that dogged his short life.

Graham Greene, Robert Byron and Bruce Chatwin (among many) all owe a debt to An Inland Voyage and The Amateur Emigrant. However, from a short list, Travels With a Donkey in the Cévennes remains Stevenson’s masterpiece, a “little book” that describes a wayward, inconsequential journey and a strange love affair (with a donkey) in which, as in all the best journeys, the author finds himself renewed, refreshed and, returning from his travels, once more ready for the fray.

Stevenson also articulates a credo that would become central to the writing of Robert Byron, Redmond O’Hanlon and many other later travel writers: “For my part, I travel not to go anywhere, but to go. I travel for travel’s sake. The great affair is to move; to feel the needs and hitches of our life more clearly; to come down off this feather-bed of civilization, and find the globe granite underfoot and strewn with cutting flints. Alas, as we get up in life, and are more preoccupied with our affairs, even a holiday is a thing that must be worked for. To hold a pack upon a pack-saddle against a gale out of the freezing north is no high industry, but it is one that serves to occupy and compose the mind. And when the present is so exacting who can annoy himself about the future?”

The brilliance of Travels With a Donkey is to keep the reader always suspended in the moment, through a combination of wry and exquisite observation and an undercurrent of delight in the pleasures of the human comedy. Here, Stevenson introduces Modestine, his celebrated donkey:

“Father Adam had a cart, and to draw the cart a diminutive she-ass, not much bigger than a dog, the colour of a mouse, with a kindly eye and a determined under-jaw. There was something neat and high-bred, a quaker-ish elegance, about the rogue that hit my fancy on the spot.”

And so RLS and Modestine set off – at her own pace…

“What that pace was, there is no word mean enough to describe; it was something as much slower than a walk as a walk is slower than a run; it kept me hanging on each foot for an incredible length of time; in five minutes it exhausted the spirit and set up a fever in all the muscles of the leg.”

However, help is at hand in the shape of a peasant saviour, a deus ex machina who, before he left Stevenson’s company, gave him “some excellent, if inhumane, advice”. This, in conjunction with “a switch” was “the true cry or masonic word of donkey-drivers, ‘Proot!’”

Sadly, the efficacy of this “true cry” was limited:

“I hurried over my mid-day meal, and was early forth again. But, alas, as we climbed the interminable hill upon the other side, ‘Proot!’ seemed to have lost its virtue. I prooted like a lion, I prooted mellifluously like a sucking-dove; but Modestine would be neither softened nor intimidated.”

So Stevenson would travel the Cévennes at Modestine’s pace, which possibly explains why his 12-day journey (something of a pilgrimage for latterday Stevenson fans) covers just 120 miles in 12 days.

It was a solitary trip, but it comes to life through the traveller’s interplay with his stubborn companion, a relationship that quickly starts to resemble a love affair:

“By the whiteness of the pack-saddle, I could see Modestine walking round and round at the length of her tether; I could hear her steadily munching at the sward; but there was not another sound, save the indescribable quiet talk of the runnel over the stones.”

Stevenson is a master of technique; he knows instinctively how to animate the most mundane moments, as in this passage when he finds himself hopelessly lost in “a random woodside nook in Gevaudan”:

“I have been after an adventure all my life, a pure dispassionate adventure, such as befell early and heroic voyagers; and thus to be found by morning not knowing north from south, as strange to my surroundings as the first man upon the earth was to find a fraction of my day-dreams realised.”

He also knows how to bring the reader close to his inner thoughts and mood:

“I lay lazily smoking and studying the colour of the sky, as we call the void of space, from where it showed a reddish grey between the pines to where it showed a glossy blue-black between the stars.”

His farewell to his travels is also his farewell to his donkey:

“As for her, poor soul! She had come to regard me as a god. She loved to eat out of my hand. She was patient, elegant in form, the colour of an ideal mouse, and inimitably small. Her faults were those of her race and sex; her virtues were her own. Farewell, and if for ever –”

Here, Stevenson shamelessly manipulates the reader with a sentimental ending, that contrives to be robust as well:

“Father Adam wept when he sold her to me; I was tempted to follow his example; and being alone with a stage-driver and four or five agreeable young men, I did not hesitate to yield to my emotion.”

Inwardly, as a writer, he was always razor-sharp; tougher than tungsten; indestructible; immortal.

A signature sentence

“I wish I could convey a notion of the growth of these noble trees; of how they strike out boughs like oak, and trail sprays of drooping foliage like the willow; of how they stand on upright fluted columns like the pillars of a church; or like the olive, from the most shattered bole can put out smooth and youthful shoots, and begin a new life upon the ruins of the old.”

Three to compare

Graham Greene: Journey Without Maps (1936)
Robert Byron: The Road to Oxiana (1937)
Bruce Chatwin: In Patagonia (1977)

• Travels with a Donkey in the Cévennes by Robert Louis Stevenson is published by Penguin Classics (£8.99). To order a copy for £7.64 go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99