Ah, so, this is what senility feels like. I’m shuffling my feet, struggling to string together five or six steps before stopping to suck hard on thin unsatisfying air. The simple act of taking a pee leaves me gasping.

As I rise past 15,000 feet on the circuitous trail around northern Chile’s Copa Coya hill, my strides shorten, my breathing accelerates, my forehead thumps. Smoke, billowing across the dramatic volcanic landscape, might be the work of local shepherds warding off pumas, or cocaine smugglers disguising their route from Bolivia, yet I barely raise an eyebrow, let alone binoculars. I’m just too exhausted.

My laborious hike is the wheezing climax of three days’ acclimatisation for an expedition that reeks of scenic and physical drama: I’m about to cross the Andes. It might sound a tad Ranulph Fiennes but the reality is far less alpha. Wilderness expert Explora swaddles the journey across South America’s spine – from Chile’s Atacama Desert to Argentina’s Salta province – in simple, stylish luxury: an iced Pisco Sour is never far away.

My Atacama base sets the tone. The chic modernist ranch, all bleached wood, squashy sofas and indigenous weaves, overlooks a horizon of 22 volcanoes, lining up either side of Licancabur’s perfect cone. Each of its four swimming pools boasts an identical white arch and cube sauna. Am I really in the world’s driest desert, 50 times thirstier than Death Valley?

It’s all very photogenic, yet the lodge pales by comparison with its surroundings. Salvador Dalí clearly had a hand in blending the hyper-saturated colours and crazed rock formations. I ease my lungs in gently at 8,000 feet, watching bright pink flamingos on Salar de Atacama’s shimmering white salt crust, before walking through the Valle de la Luna, where orange cliffs rise between black sand and cyan sky. Sunset alchemises the whole lot into liquid gold.

Each day’s excursion lifts me 3,000 feet higher. I hike up the Puritama, more a trickle of perspiration than a river, marked by swaying pampas grass. The local humour is as dry as the canyon’s rock. ‘My nose is really running,’ sniffles a fellow guest. ‘Is it the altitude?’

‘Could be,’ deadpans my guide Chino, as he clambers over a boulder. ‘Or perhaps a tumour.’

The reward for reaching the top of a ladder of thermal pools is a fluffy Explora bathrobe for a warm muscle-relaxing plunge, and a very welcome gourmet picnic. Served on a gingham tablecloth in the middle of the desert, it’s the most surreal sight so far.

My final day’s acclimatisation reaches the Altiplano (land above 13,100 feet) where the Tatio Geysers are the highest on Earth. Every nine minutes the bleak ice-flecked plain gurgles, hisses and erupts with jets of scalding steam and boiling water. Welcome to the apocalypse.

A closely monitored walk around Copa Coya and my lungs get the green light. It’s time for the Andes. Purists look away now. I’m not tackling the mountains on foot. Instead, I’ll drive along an old trading route, interspersing the road trip with memorable walks.

At Chile’s final immigration post, a yellowing poster displays a missing person with alarming scars and Javier Bardem eyes – I fear he’s feeding the flamingos. The Argentinian border lies 125 savagely beautiful miles to the east. After bisecting purple-black plains dwarfed by volcanoes including Lascar’s smoking cone – it last vented in 1993, throwing ash 1,000 miles onto Buenos Aires – I cross the original Inca Trail.

An hour later the road suddenly rears up. I’m pushing into the high Andes. At 14,000 feet, I stop. Hike time. The wind chill is -15C but who cares? Before me a ring of cappuccino-hued peaks, their summits streaked with sulphur, salt and snow, encircle an emerald lagoon among red plains frescoed with yellow scrub. Hallucinogenics are not required.

“Every nine minutes the bleak ice-flecked plain gurgles, hisses and erupts with jets of steam”

A walk, many photographs, an exhilarating drive and I reach Chile’s frontier police station: a corrugated iron hut taunted by sub-zero gusts. ‘We go for weeks without seeing a car,’ reveals a khaki-clad officer. ‘If it snows, we’re stuck.’

Ten brutal miles of no-man’s land and the mood darkens. A scowling Argentinian official, newly arrived and ravaged by altitude sickness, listlessly stamps my passport beneath a poster offering $100,000 bounty for information about four moustachioed kidnappers.

No words are spoken. No eye contact offered. Some welcome. My journey continues, descending into a rumpled quilt of chocolate and mustard hills. Sights start to blur: disused rails that once carried ‘The Train to the Clouds’, a plain specked with vicuña, a scattering of sleepy hamlets.

In rapidly fading light there’s one final white-knuckle climb over a 16,000-feet pass – I stop counting at the 90th switchback – before
I stumble into Explora’s campsite. The tents have silk sleeping bags, alpaca wool blankets and chocolates on the pillow. Forgive me, Sir Ranulph.

Rested, restored, spoilt rotten, I take an early morning hike before driving along the rutted R40 ‘highway’ from Patagonia as it follows the Calchaquíes River. The Nile-like ribbon of fertility widens before my eyes, surging swathes of red rock with Inca granaries carved into its cliffs like a South American Petra.

As I drop, the mercury rises. It’s frying by the time I reach Cachi for two nights in a finca with a bathtub overlooking the vast Calchaquíes Valley. I’d happily spend weeks here, exploring forests of cactuses, wandering around Cachi cemetery’s house-like tombs and sipping cheap cervezas as vintage Chevvies cruise around the central square.

Time, sadly, interferes. The final descent off the high plateau at Piedra Del Molino is astonishing: a 35-minute, 6,500ft drop on a snake of a road straight into a sub-tropical world. Salta has accordions playing wistful Argentinian melodies, creeper-clad trees and lush lawns. The sudden contrast to barren rock is both brutal jolt and chequered flag. My journey’s over. I’ve just crossed the Andes.

Explora’s Andes traversia, including stays in the Atacama Desert and Salta, plus three full-board nights on Easter Island, costs from £20,000pp including all flights, transfers and excursions; abercrombiekent.co.uk

Images: Getty Images; Alamy