Emile Hirsch, Vince Vaughn, Catherine Keener, Kristen Stewart, William Hurt, Marcia Gay Harden.

Running time: 140 minutes.

. . . .

IN 1990, university graduate Christopher McCandless had a dream. It was simple. He would cease all communication with his family, donate his $24,000 savings to charity and disappear. So he did just that.

He abandoned his car, burned what few dollars he had left, and broke his family's hearts. That was the beginning of his great adventure, a trip that was to take him to the wilds of Alaska. There, he sought to forget his old self and find spiritual commune with the wilderness.

He ventured out with no experience and few provisions: 10lbs of rice, a .22 rifle, a book about edible plants, and a troubled personality.

But who needs carbohydrates when you are fuelled by a naive idealism from the books of Henry David Thoreau and Jack London, whom Christopher read over and over again. Into The Wild takes the true story of Christopher McCandless (played here by Emile Hirsch), as told in Jon Krakauer's bestselling book, and both celebrates and dismantles the myth of the wild as a place of simplicity and rebirth. Writer/director Sean Penn shows us an extreme personality, running as fast and as far away as possible from himself, to become both hero and tragic figure.

Another film, Werner Herzog's penetrating documentary Grizzly Man, explored a similar issue. Herzog (another extreme personality who once forced a film crew to haul a steamboat up a jungle hill) put together the remaining video footage of bear enthusiast Timothy Treadwell, a naive man who lived on the edge in Alaska with wild grizzlies. They ended up eating him. Herzog wanted to know why Treadwell put his life on the line.

Grizzly Man was full of the simple joy found in Treadwell's video footage, summed up by an enthralling shot of a tame fox dancing on the wet roof of Treadwell's tent. Here, Penn gets caught up in Christopher's romantic idealism. The camera at times becomes lost in spiritual rapture. And I'll admit there is something tantalising about losing yourself to the wilderness, the suggestion of a return to something fundamental.

This enthusiasm peaks on a mountaintop, when Christopher stands, arms outstretched, like the statue of Christ on Rio De Janeiro's Corcovado mountain. The camera pirouettes 360 degrees around him, and I waited for the cloying music of a Bord Failte ad to kick in.

But Penn is also luring us into the dream, exploring the fine line between fearlessness and madness.

The mythological space of America's frontier was always a place to find yourself or to reinvent yourself. Christopher's parents, played by William Hurt and Marcia Gay Harden, were products of the American dream, but the pressures of sustaining it ripped their marriage apart. We witness flashbacks of violent dysfunction, leaking like sewage into their children's lives. Christopher's sister Carine (Jena Malone) tells us in voiceover that this is what Christopher wanted to forget by reimagining himself.

He changes his name to Alexander Supertramp and hitchhikes across America. He harvests grain with a bubbly farmer called Wayne (Vince Vaughn); he lives in the back of a camper van with ageing hippies and learns leatherworking from kindly retiree Ron (Hal Holbrook) who offers to adopt him. We see Christopher begin to open up and to be accepted, before continuing alone to Alaska. But mother nature, less understanding, couldn't care less about such idealistic notions.

Christopher carried his books with him everywhere he went. But if he'd watched more movies instead, he might have anticipated how harsh the wild can be. He might have seen how Charlie Chaplin was forced to eat his boots in the Alaskan Klondike of The Gold Rush. Or Robert Flaherty's Nanook of the North, which showed us the Inuit Nanook struggling to provide for his family in Canada's snowy Ungava Peninsula. A hunter by birth, Nanook died of starvation after the film was made. Middleclass by birth, Christopher McCandless, was equipped with a degree in history and anthropology. What chance did he have?

This is Sean Penn's fifth movie as director and comes in the tradition of the great American movie . . . a spirited adventure carved from America's epic landscape. But what makes it resonate is how it shows that recklessness can be both inspiring and plain idiotic; how extreme personalities are very often wounded children.

Emile Hirsch, seen recently in Alpha Dog, transforms in the role.

His round, pink face, framed with a frizzy beard, is a cicatrice of inner pain that soon wanes with hunger.

His muscular build falls off him.

His Christopher quotes the famous Thoreau line: "Rather than love, than money, than fame, give me truth." But Into The Wild demonstrates how easy it is to ignore the truth. Christopher confuses being at one with nature with being at one with himself. It was a very dangerous mistake to make.