In Chapter 29 of his book Wild Wales, published in 1862, George Borrow, a six-foot, 59-year-old Englishman, describes reaching the summit of Y Wyddfa, the highest point in Wales, eight years earlier. He considered it to be not just the most beautiful, but also the most romantically evocative mountain in the entire world. He was a newcomer to Wales, but he was already widely travelled in Europe and he was also a passionate linguist and antiquarian.

This is what he did when he reached the summit. At the top of his voice he recited two stanzas in the Welsh language consisting entirely of vowels and the single consonant R. Three or four English bystanders, Borrow tells us, looked on ‘with grinning scorn’ at this performance, but the solitary Welshman up there walked over and warmly shook his hand.

Such is the book Wild Wales, all over. To this day it is without doubt the most celebrated book written in English about Wales – its ‘People, Language and Scenery’, as the subtitle tells us. Like its author, though, it is anything but conventional. Least of all is it a travel book, as it is too often called. At its heart is indeed a walk that Borrow did from the north of Wales to the south, but it was a hugely unstructured, often unmapped kind of walk, full of detours, backtrackings, changes of route and spontaneous decisions. Part of it he undertook in the company of his beloved wife and stepdaughter; more often he was cheerfully and sometimes bibulously (for he loved his ale) alone.

Nor is it, by any means, propaganda for Wales. Borrow lost his heart to the little backwoods country, but he loved it warts and all, and he never adapted his behaviour to its style – never became neo-Welsh himself. Nor does his book pull its punches. It is a work sometimes delightful, sometimes maddening, just as Borrow himself could be variously irresistible and insufferable.

So Wild Wales is not a portrait of a country but an evocation of one man’s responses to a country and its people. You may well be topographically and even historically confused if you try to follow Borrow’s itinerary, but you will have spent, as it were, a few hundred intimate pages in somebody else’s very different mind, as he does the travelling for you.

Writers are notoriously self-centred, I know, but you will perhaps forgive me when I interrupt myself here to say that achieving this effect has always been the purpose of my own so-called travel books, and that I have accordingly read and reread Wild Wales, down the decades, with extra empathy. It does not mean that I always admire what I read. Borrow’s egotism is sometimes unbearable and he can be a show-off of the most irritating kind. Intellectually, too, he is beyond my league: he was an instinctive linguist, a profound student of history and an indefatigable scholar. It does mean, though, that as an Anglo-Welsh writer myself and an addict of the numinous spirit of Wales, the hiraeth that has variously inspired its poets and its people down the centuries, I always know, as they say nowadays, where Borrow is coming from. I might not be able to recite those weird stanzas on the summit of Y Wyddfa, but I too would certainly have walked over and shaken the traveller’s hand.

George Borrow had taught himself a smattering of Welsh in boyhood with the help of a Welsh acquaintance, but he had learned a good deal more since, and in a way this knowledge created Wild Wales. That episode on Y Wyddfa was a narrative apex, too, because it was a summation of the book’s main theme.

It concerned above all Cymraeg, the Welsh language. It was an extraordinary thing in 1854 for an English tourist to understand any Welsh at all, let alone converse in it, and Borrow made the most of this. He enjoyed the surprise of Welsh people when he revealed that he understood their conversations, and he delighted in displaying his superior knowledge of ancient Welsh history and poesy to wondering natives. Much of the book is constructed around this particular relationship, and to my mind it has in it a faint echo of complex interactions between imperialists and cultivated indigenes in the wider British Empire. (We may perhaps wonder about the merit of his boasted translations from classical Welsh, if we take this couplet from the great medieval poet Dafydd ap Gwilym as an example: ‘In every hollow dingle stood/Of wry-mouth’d elves a wrathful brood.’)

On occasions his behaviour can make one squirm: he is sometimes patronising, sometimes downright deceptive and nearly always too pleased with himself. But technically, I realise, the approach was very effective. Often enough, having antagonised somebody with his attitudes, reconciliation has given him new insights. Even in print, having momentarily alienated us, his 21st-century readers, a sudden flash of kindness, understanding or sympathy can instantly warm us to him again, as glimpses of his better self so often warmed total strangers in his own time.

Whatever his mood or his manner, he was inspired always by his feeling for that other Wales, the ancient Wales of the legends and the poets – the inner, half-imagined world of hiraeth that seduces me too. The ancient Welsh language lay at the heart of hiraeth, but its complex and lovely seductions were everywhere then as they are now.

This is how the dear man behaved when he reached the bare moorland summit of Plynlimon in mid-Wales. The sources of three rivers famous in Welsh fable and history are all within a few miles of each other up there, and Borrow decided that, for poetical or perhaps symbolical purposes, he must visit them all. Furthermore, he decided that he must ritually drink water from each of them at the place where it first reached the air of Wales (he was as big on water as he was on beer). He and his guide tramped across the soggy grassland from the Severn to the Wye to the Rheidol, and Borrow drank from all of them, until the patient guide assumed that the job was done at last and that they could go down the mountain to supper and bed. But no. Borrow took off his hat and sang a poem written, he said, by a visitor to those springs four hundred years before.

Bless his heart. He walked home to his lodgings that evening, he tells us, with a bounding and elastic step, and ‘could never remember to have felt more happy and cheerful’. It was the indefinable essence of Wales itself that had done this for him, as it often does for me, and it infuses his Wild Wales, too, with a kind of happiness that is all its own.