Known officially as Ruta Nacional 40 (RN40), the Patagonian Highway runs nearly the length of Argentina, a distance of more than 5,000km. In the north of the country, it begins just south of the Bolivian border and continues almost to Tierra del Fuego in the south.
To do the full trip requires a combination of vehicles, because much of the road is unpaved. Some stretches require just a regular car, others need a 4x4. Of course, walking is an option for part of the way, in which case good shoes, plenty of food and water and an appetite for adventure are essential.
With the exception of the hubs of El Calafate and El Chaltén, rutted Ruta Nacional 40 is a no-man's-land. It parallels the backbone of the Andes, where ñandú birds flit through sagebrush, trucks whip up huge storms of whirling dust, and gas stations dominate the horizon like oases.
Nonetheless, the paving of RN40 is under way, with long stretches of the road smooth enough for cycling. Still, if you want to experience this lonely highway at its most evocative, get there quickly before the renovation is complete. Its raw state is, after all, the mythical road to nowhere that has stirred the loins of many, including Butch Cassidy and the writer Bruce Chatwin.
The paving of RN40 will clearly end this identity, which has defined a generation. When the reconstruction is finished, most motorists are likely to whiz from sight to sight, bypassing the quirky, unassuming settlements that provide so much joy for connoisseurs of the trip. For the moment, public transport stays limited to a few summer-only tourist shuttle services, and driving requires both preparation and patience.
THE JOURNEY TODAY
You've been on the road for a week and everything about the trip has been monumental, including the repairs. Gravel punctured your petrol tank a while back, and you dodged flying rocks and sheep that think they own the road.
You've negotiated blind curves on windy days when it seemed your car would fly right off the road, and all the while you've been struggling to process the sheer amount and variety of experiences that have come your way. You've seen massive frontier horizons dwarfing the gauchos that ride their horses on the steppe, and you've imbibed the monumental silence that accompanies such a space – a wild, barren emptiness as thrilling and as awesome as the craggy peaks and unspoiled rivers.
Now you've arrived in Patagonia itself. The map tells you it's a very large place and you've seen that for yourself. It's almost a country within a country with its oil boomtowns, petrified forests, spectacular Península Valdés and splendidly isolated Welsh settlements. You've heard about the trendy Patagonia, too: the tourist hubs with designer shops which seem worlds apart from the RN40.
But it's been hours since the last town. You've been driving for what seems an eternity. The weather is cunning and the gravel dastardly. You're not in a hurry because the conditions won't allow you to be.
Your car is rattling, as are your teeth, as you trundle along this bumpy stretch. But then, a magical moment: the view ahead suddenly cracks apart with brilliance and radiance as glacial peaks and gem-coloured lakes make their presence felt with preternatural charm. And then it hits you, like a flying rock from the side of the road. This is why you came.
The Patagonian stretch of the RN40 provides a potted summary of everything that makes the journey great. Through inland Patagonia, highlights include the Perito Moreno and Los Glaciares national parks, the rock art of Cueva de las Manos and remote ranches. The iconic character of the road is also intact – from Esquel, it continues paved until south of Gobernador Costa, where it turns to gravel. From there on it's mostly gravel, with slowly increasing numbers of paved sections, mainly near population centres.
Extract from Great Journeys, published by Lonely Planet (£29.99). Readers can buy a copy for £25 including UK P&P by going to shop.lonelyplanet.com and using the code INDEPENDENT
* Become mesmerised by the magical, blue-hued Moreno Glacier, and be entranced by icebergs crumbling – each time with an almighty boom.
* Step back in time to explore the wonderful millennial forest in the Parque Nacional Los Alerces.
* Accept the challenge and trek the exciting Fitz Roy range near El Chaltén.
* Commune with nature and enjoy the sight of southern right whales up close in the waters of the Reserva Faunistica Península Valdés.
* Play the gaucho by riding the wide-open range and feast on fire-pit roasted lamb at a traditional estancia (ranch).
Argentina's Patagonian Highway
Distance: 5,000km Countries covered Argentina
Ideal time commitment: One to two months
Best time of year: December to March
Essential tip: Assuming you feel safe to do so, always offer to help anyone who you see stranded on the side of the road; there's no roadside assistance and mobile phones don't work in the area.