It’s 9am on a cloudy Tuesday. A pick-up truck arrives in a remote parking lot in California’s Joshua Tree National Park, hauling a pristine vintage Airstream trailer. On the driver’s door is written “LP Ranch, Angus Cattle, Mertzon, TX”. Inside is a little two-room travelling boutique hotel. A dreamcatcher hangs over a quality bedspread. There’s a stainless-steel fridge. A bumper sticker reads: “Solidarity/Unity — International Brotherhood of Boilermakers”.

A surfboard is marked “Malibu”.

Matthew McConaughey is in the driver’s seat wearing a plaid lumberjack-style shirt, chewing a cinnamon-scented toothpick. He co-owns that faraway Texas ranch and occasionally uses it as a “hideout”, he says, but lets a cousin run it.

McConaughey has more glamorous setups, either in Malibu with his Brazilian model girlfriend, Camila, and their baby, Levi, or in this Airstream, wherever his whims might take him.

He whips off his sunglasses and flashes a wry, slightly unhinged smile. “Let’s do this!” he says. He leads the way down a nature trail next to Cap Rock, an enormous pale boulder that sits amid the eerie vegetation like a bauble of the gods. The walk, safe for toddlers, seems beneath him. His tough exercise style, where everything is a triathlon-training session or a scramble up the steepest slope, has left many seemingly fit buddies gasping in the dirt. But not today, McConaughey says. He’s in conservation mode. Eight days ago, he hit the road for a 10-day fast, ending up in a remote spot in the middle of low-lying desert outside Joshua Tree.

With his family back in Malibu, McConaughey is taking this trip alone. “It’s a good time to take a little inventory, work on some prudence,” he says. He’s spent most of his time entering old notebook diaries of his travels into his laptop — a chance to reflect and stare off aimlessly into the distance. Only water, tea and broth have gone into his system since he started. Ten days is not a big deal. The human body has enough energy to last 40, he says. “I’m high and clean and tight, man. It’s good to feel hungry. If you keep filling your tank when it’s three-quarters empty, you’re gonna run on old fuel. So you gotta drive it down to empty and let it work. I came here to press a little reset and then head back down the road.”

McConaughey turns around, spits into the brush, unzips his trousers, and lets the piss fly. When that’s done, he pops in a piece of gum. He chews it lovingly. “Dessert,” he says.

In addition to his film work, McConaughey has several businesses — a clothing line, a record label, an indie-film production company — but the road is where he finds meaning and purpose. The trips he’s taken over the years have framed his life, helped define him. “He’s always on the road,” says Mark Gustawes, his old frat brother from the University of Texas, who helps to run his production company, j.k. livin’ (as in, “just keep”). “I don’t think people actually believe he does it. But it’s the truth. He’s a total vagabond.”

It’s 1980, and Big Jim McConaughey, a travelling oil-pipe salesman based in Longview, Texas, has to collect a payment from a client in Houston, a good 210 miles away. He brings along the youngest of his three sons, 11-year-old Matthew. Big Jim asks Matthew to put on his nicest jeans and shiniest boots. They make the trip in five hours. Big Jim calls upstairs. The client’s secretary says he’s not in. But this man’s been dodging calls for weeks, so Big Jim takes Matthew up in the lift. They walk past the secretary into the client’s office, where he’s sitting at his desk. Big Jim introduces his son. Big Jim is a physically imposing man, but he still thinks it’s going to be a lot easier to collect with the kid in the room.

That run works so well that Big Jim brings Matthew on half a dozen more trips. They drive to Oklahoma, Louisiana, Mississippi and all over Texas. One time they stop in New Orleans for a shrimp festival. Another time, Big Jim slinks behind a low-rent Louisiana mall and buys a titanium Rolex from a man selling appliances out of the back of his truck. “I thought that was cool, man,” McConaughey says now. “Getting out of the backyard and seeing these trails my dad cut. Seeing people he’d met along the way. He always said, ‘What’s out back? I know we’re way off road, and we’re dealing with some shady stuff, but I want to see stuff that’s even shadier.’ ”

Big Jim was 41 when Matthew was born — a surprise baby — and these trips bring them closer; they are some of the best times they have together as father and son. Big Jim lets Matthew play navigator. They get a bucket of KFC and eat the whole thing. They talk about “life and chicks”, and Big Jim, a passionate man who would divorce Matthew’s mother twice and remarry her twice, gives his son some advice. “Now, you’re getting to the age where you’re gonna start messing around with girls,” he says. “So here’s what you’ve got to follow. You’re going to get close, you’re going to get intimate. If you ever make a move and you feel the slightest bit of resistance, stop. A lot of times, after you stop, they’re going to then say, ‘Now it’s okay.’ Don’t. That time, that day, that’s as far as you go.”

This advice will pay dividends for the future Sexiest Man Alive. “It’s a great lesson,” he says. “You do that, and you know what? Women come back. They say, ‘What? Nobody stops!’ They want to go out with you again. And eventually you don’t have to stop.” He looks forward to sharing this with his own son when the time is right. Road-trip wisdom, he says, should be passed on.

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