Every city-dweller knows the sensation of feeling imprisoned within an urban world of brick and glass. Sometimes it's triggered by a jam-packed thoroughfare in a shopping precinct. Often it is heralded by a crowded train carriage deep underground.
But the next time you find yourself mired in dark thoughts about the soul-blanching impositions of city life, walk straight into the nearest bookshop and buy a copy of Robert Macfarlane's The Wild Places, his erudite and exquisitely written follow-up to his acclaimed debut, Mountains of the Mind. The book is balm for the most acute metropolitan malaise.
Its premise is simple. Macfarlane, a young Cambridge don, decided to make a series of short journeys to establish whether anywhere in the British Isles can still be described as "wild". Surely, in a country in which more than 63 million people jostle for space across a paltry 120,000 square miles of land, such a concept cannot exist?
Macfarlane's quest takes him to far-flung nooks across the British archipelago, from the gentle beechwood coppice just a mile south of his Cambridge home, to the vast and trackless expanse of Rannoch Moor, to the snow-and-ice asperity of the summit of Ben Hope in northern Scotland, to the labyrinthine network of sunken roads or "holloways" snaking across Dorset.
Each of the book's 15 chapters is devoted to a different trip. On most of them, Macfarlane spends at least one night out in the open, and picks up a memento: a pebble, a willow catkin, a kestrel's feather, a few blades of moor grass.
Interspersed through the narrative are shards of cultural history, geological exposition, travelogue-like observation and essayistic analysis. There are riffs on a range of subjects, from the monks and anchorites who settled on the remote coasts of Britain and Ireland between AD 500 and 1000, to the reputation of seals in folklore as "in-between creatures, half-human and half-marine". These lend the work a pleasingly digressive, provisional aspect, so that it resembles a commonplace book of the natural world.
That said, very little is provisional about the prose. Macfarlane writes with beauty, lucidity and skill. His vocabulary is satisfyingly wide-ranging, never deliberately abstruse or pretentious. He works hard at metaphors and similes, whittling them until they are just so: wrinkled beech-bark "resembles the skin on an elephant's leg"; winter sunlight is "so bright that it lay in ingots on the riverbed".
The sentences are awash with images that deliver little jags of pleasure. Here he is leaping into the sea off the westernmost tip of the Lleyn peninsula in North Wales: "I dived in. Blue shock. The cold running into me like a dye." That commingling of colour and temperature jolts us into experiencing the gelid seawater for ourselves.
But as well as myriad examples of burnished writing, the book also teems with insight. As it progresses, Macfarlane's conception of what constitutes wildness starts to shift. At first, he imagines wild places as remote and figureless, outside human history - a frost-shattered summit, say, or a corrie holding a deep loch. He cites a batch of writers who have declared wildness dead in Britain and Ireland, as well as statistics aplenty detailing the denudation of Britain's wild places (half a million acres of broadleaf forest were felled between 1914 and 1918 to meet war needs, for instance).
In the second half, though, he begins to recognise a different but just as potent model of wildness: a vision of riotous vegetable fecundity scored with the ley lines of human history. The deep-set "holloways" of Dorset, fizzing with thick organic growth as well as their history as the hideouts of fugitive Catholic priests in the 16th century, provide an excellent example of "an unexpectedly wild world, buried amid the familiar and close-at-hand". "The human and the wild cannot be partitioned," he suggests.
Macfarlane also makes a convincing case that wildness and the imagination are essentially entwined. He believes in a correspondence between inner and outer landscapes. This prompts a cultural, as well as environmental, case for preserving wilderness in Britain: without it, he argues, we lose valuable modes of thought.
Throughout, Macfarlane is spurred by a childlike sense of wonder and discovery. His title echoes Maurice Sendak's 1963 classic children's book, Where the Wild Things Are. He is always climbing trees (silver birch, alder and young cherry prove usefully supple in this regard). Traversing dense, snow-bound "wildwood", he thinks of John Masefield's The Box of Delights and the frozen forests of the Snow Queen's Narnia. During a nocturnal swim in a Welsh bay that glows with phosphorescence, he finds that he can fling streaks of fire from his fingertips, "sorcerer-style", "so I stood in the shallows for a few happy minutes, pretending to be Merlin, dispensing magic to right and left".
Playfulness permeates this book, conjuring a sense of innocence that suggests - perhaps surprisingly, in this doom-and-gloom age of environmental concern - that all is not lost.
"There is no forest or fell to escape to today, no cave in which to curl up, and no deserted valley," wrote E M Forster - and that was in 1964. But anyone who feels oppressed by man's seemingly indelible imprint on the land must read this book: the hidden headlands, cliffs, beaches, mountain-tops, tors, forests, river-mouths and waterfalls which Macfarlane writes about suggest that wildness hasn't wholly vanished from Britain. "The wild prefaced us," he concludes, "and it will outlive us."
Alastair Sooke works for the Daily Telegraph