Richard Long walks for Art. Across the Sahara, the Himalayas, the Scottish highlands. And now the innocent abroad has tramped through the Mafia lands of Sicily, creating mud drawings and stone sculptures, to become a local hero. Jonathan Jones falls in step.
We were coming into Palermo from the airport when someone pointed out the place where Giovanni Falcone was blown up by the Mafia in 1992 for his campaign against organised crime, here on the motorway, beneath a looming rocky hillside. Judge Falcone's death has become part of the landscape of Sicily. The nondescript spot where he died has been absorbed into the island's mythology along with The Godfather, and the lake where Persephone was dragged down into the Underworld. This is the blood-soaked Arcadia into which the artist Richard Long walked.

"Richard's walk actually takes him through Corleone," his press agent told me, "but he didn't think that should be mentioned on the press release." Richard Long is an unworldly man. He would never contrive a publicity stunt. It occurred to me that for 30 years he's been doing what Samuel L Jackson vows to do in Pulp Fiction, just walking the earth having adventures, like in Kung Fu. He looks the part, a tall, gaunt figure with bushy eyebrows and a little round-brimmed sunhat, wearing a check shirt and drainpipe jeans, part preacher, part cowboy. When he works on a sculpture, he wears a bandanna depicting the Kyoto rock garden that expresses his affinity for Zen Buddhism.

"The fact I had a few days spare to make a three-day walk across Sicily, that by chance took me through the epicentre of the Mafia world, which is Corleone - that's complete coincidence," explains Long when I meet up with him in Palermo. "But since I've come to Sicily, it's good to use my walking energy and water energy in the mud circle and my stone energy."

Richard Long's self-effacing art covers vast areas of the planet. He's transformed entire landscapes, including the Sahara, the Himalayas and the Scottish highlands, into works by Richard Long. Yet only by the luckiest of coincidences will anyone travelling in these territories find any trace of his passing. Long is in a tradition of English explorers, laying claim to land on behalf of his distinctively English aesthetic, and at the same time disappearing into the earth he walks on. He told me how he was kidnapped, probably by Kurds, while walking in eastern Turkey and bundled into the back of a truck with animals. He thought he was about to be killed. Instead he was taken to a village in the mountains and fed an enormous meal while the villagers looked on. Then he was dumped at the nearest bus-stop and told never to visit that part of the world again. Long's art replaces the painted landscapes of Richard Wilson or Constable with his own dangerous journeys, always with the possibility that he won't come back.

Thames and Hudson have just published Long's book, A Walk Across England, but I caught up with him miles away from anything like a launch party, working on an exhibition in a former aircraft hangar on the outskirts of Palermo. "I ticked the box marked `No Publicity'," he jokes about his reluctance to give interviews. He's not an easy man to get close to and, after following him around for a couple of days, I started to feel like the stray kitten he allowed to clamber about on the sculpture he was making, tolerated and indulged. My first glimpse of the inner Long came when I watched him climb a tree.

We'd just finished lunch in Piazza Marina, a Palermo square lined with crumbling 17th-century palaces. Someone suggested coffee but Long wanted to be moving. We walked across the square and Long stopped underneath a giant, ugly tree. Suddenly he climbed on its thick roots and clambered inside a hollow in the trunk, forgetting everything else in his single- minded enjoyment of nature. Richard Long is a wild man, more at home in a landscape than among people.

"For me, solitude and independence are very energising," he says, when we are chatting later in an apartment full of Italian street noises - whizzing scooters, honking car horns, rows. "It's very relaxing and it's imaginative and it's a great state of mind, despite all the hardships and foot soreness and wind and rain and all the stuff you get on any walk." The perfect moment on a walk, the revelation he searches for, is that sense of "being one-to-one" with a landscape, "so there's no intermediary stuff like using machines or social company. It's a kind of purity."

Richard Long is not the first person to associate walking with solitude and nature-worship. "There's a whole history of walking," he reminds me, "not only in English culture going back to the Romantic poets - Wordsworth was a great walker, and Coleridge - but in most cultures of the world." Yet no one has done it quite like Richard Long. "I'm proud of the fact that when I made my first 10-mile straight line across Exmoor, no one had made a walk like that in the history of culture. I've been able to invent a completely new way to make walking into art."

Long's way of walking belongs to the late Sixties. His generation rejected Pop art and its celebration of the consumer society. They chose instead to go "underground", as he puts it, and rethink the nature of art. "It was a very imaginative, idealistic time," Long tells me, "that's just a fact. It's that moment in history when the whole language of art could be reinvented, and it was reinvented through Conceptual art, Minimal art, Performance art, Land art." He started making walks when he was a student at St Martin's in 1967 and 1968; these works instantly made sense in the climate of Conceptualism. Yet he'd been doing much the same thing all his life, almost compulsively, before he knew anything about the international avant-garde. It's not insulting Richard Long to call him a naive artist. "There was never a point where I became an artist. When I was a young kid, I was always drawing and painting all over my bedroom walls - I used to make mud pies and stuff. Art keeps me in touch with my childhood. I still skim stones across rivers, and the great thing is I've been able to use it to make art."

Only an innocent would plan a walk from Palermo on the north coast of Sicily to Agrigento on the south coast without considering that it would take him through the Mafia's heartland. Long doesn't do research; he seems to avoid reading guide books or histories of the regions he visits. He tells me he didn't know Sicily had ancient Greek ruins until he got there. "All my work is about making my own history in the landscape," he says. A detailed knowledge of Sicily's labyrinthine past, from the Cyclops' cave to the arrest of Mafia capo di tutti capi Salvatore Riina in Corleone in 1993, might get in the way of confronting the landscape directly. "It's about that immediate physical engagement with the world, whether it's the size of a country or the size of a stone."

This direct physical engagement with the world, precisely because it frees Long from ready-made expectations, unlocks the poetry of landscape in unsettling ways. One of his heroes is John Cage and, like Cage, he's fascinated by the music of chance. His walk from Palermo to Agrigento tapped all kinds of historical and mythic substrata. He filled his bottle with water from a cemetery tap at Piana degli Albanesi, near the mountain pass where Salvatore Giuliano massacred Communist sympathisers on Mafia orders on May Day, 1947. He was menaced by a pack of wild dogs between here and Corleone. In the notorious Mafia town itself, he was watched by groups of men sitting conspiratorially. The very movement of Long's walk from north to south - downwards, from the top to the bottom - conjures a descent into the Underworld that, in ancient myth, lies beneath Sicily.

Long evoked the mouth of the Underworld again when he painted a gaping black circle, 19 metres in diameter, on the floor of Spazio Zero, the art space in Palermo where he currently has an exhibition. Long's gallery works, his stone sculptures and mud drawings, imitate the scale and power of landscape. His black hole on the ground was an abyss, a void, the way to Hades. I watch him as he throws mud from a bucket to cover up this darkness.

"Sicily is promoting culture as the antidote to its Mafia history," he tells me, "which is great." He's become a hero to Sicilians. He was invited to the island for Palermo's Festival of the Twentieth Century along with Peter Greenaway and Harold Pinter. Their work went down well but Long was undoubtedly the star; we went to a restaurant one night and he was feted by the management while Pinter waited for a table. Sicilians responded with such intensity because Long's art has direct significance for an island desperate to cleanse the blood from its landscape. He is helping Sicily to exorcise its demons, simply by going for a walk across a landscape that still frightens foreigners and locals alike with stories of kidnappings and murder. For Richard Long, this was just another adventure on his journey. He's been walking all his life and he shows no sign of slowing down, of hanging up his boots and staying at home in Bristol. Perhaps one day he'll just vanish down the road.

Exhibition: Spazio Zero, Palermo, Sicily (0039 91 7434341) to 15 January 1998. Book: `A Walk Across England' published by Thames and Hudson, pounds 18.99