The last thing I remember hearing as I whizzed down the slope was "sin miedo!" It's Spanish for "fearless", but Pablo, my guide and an experienced mountain-biker, meant it as a command. From behind, he could see I was wavering as I entered the last bend and as so often happens at moments when your cojones are being tested the main risk to my well-being was hesitation.
Pablo flashed past. So I pushed harder on the pedals and hit the hairpin bend at full tilt. My eyes blurred with water and g-forces, and I was, for a moment, completely senseless my body was moving too fast for my vision and sense of balance to keep up.
Somehow I made it to the bottom. We'd been trying out a new mountain-bike circuit on an idyllic estancia called La Usina and, as a reward for testing the circuit, we were treated to a delicious lunch of lamb and trout empanadas, Hereford beef steak, Argentinian red wine and some highly calorific desserts.
I needed the fuel. I was in the Parque Nacional Los Glaciares, Argentina's adventure-tourism playground. For most of the year, it's a cold, inhospitable corner of the planet. But from November though to April it is temperate, even balmy, with long cloud-free days, and blooming red firebush and other native flowers everywhere. Consequently, this 7,000 sq km zone of Andean peaks, crystalline lakes, glaciers and ice fields fills with hikers, bikers and climbers. Nevertheless, as the "glaciares" bit of the name suggests, this is no ordinary topography and the weather can be, well, changeable.
El Calafate is the hub for exploring the lakes and glaciers at the southern end of the park. The town itself has all the restaurants, bars and hotels you could need, but looks improvised. It spreads untidily across a wide valley, evidence that it's a base for seeing beautiful things rather than an attraction in itself. On one side is the immense, turquoise-coloured Lago Argentino a lake that extends all the way to the Andes and the Perito Moreno glacier and on the other, a treeless, dun-coloured valley bottom and then a steep slope rising to dramatic, arid tablelands: the definitive Patagonian landscape. You'll rarely come across a vista where the contrasts are so crude and yet so dramatic.
The harsh grasses and thorny brush of the tablelands present forbidding terrain. Pablo and I hooked up with Lucho, a former mountain guide and skilled 4x4 driver, who drove us to El Calafate's southern flank in his Land Rover. If it was barren-looking on the edge of the town, up here was true desert, littered with huge "erratics" boulders dumped by receding glaciers aeons ago. Lucho explained that we were actually driving across a 180-million-year-old riverbed, pushed upwards when the Andes were forming. Pumas live here, and although we didn't see any (they are almost impossible to spot by day) we did make out some puma tracks at the bottom of a crevasse. At the edge of a high cliff we observed condors; this is the optimum altitude for observing them as they drift past, wings unmoving, heads fixed and intent as they searched for lost lambs and new carrion. To the west, we could see the peaks of Chile's Torres del Paine.
El Calafate is only an hour's drive from the lake glaciers that emanate from the great southern ice field of the Patagonian Andes. The Perito Moreno glacier, named after the Argentine explorer Francisco Moreno, is one of the country's greatest natural wonders. People are drawn here by the beguiling beauty of the ice, along with the setting: dramatic mountains, ancient beech forests and strange skies full of bizarre cloud formations. The microclimate is caused by the sheer heft of the ice. The glacier covers a larger surface area than that of Buenos Aires; the ice field is about the size of Israel.
Three years ago, the Perito Moreno made front-page news round the world when its front portion collapsed and went crashing into the water below. But the front wall of the glacier is calving breaking off in huge chunks all the time. As the boat I was on approached the glacier's rocky moraine, I saw fragments of sparkling azure-coloured ice fall into the cold lake below. Seconds later I heard the sound of an almighty splash.
To explore the Perito Moreno, you can take luxury cruises, do short treks or join groups on what is called the "Big Ice": a tough, day-long hike over tricky terrain. As the Land Rover and the bicycle had done most of the work to that point, I opted for the latter. A fast, steep climb took us along the rocky edge of the moraine, after which we donned crampons and were led by our guides into the cold heart of the glacier.
It was a wonderful, invigorating amble you can't but amble in crampons and it took us across the weird wave-like surface of the glacier, fording streams and leaping over the narrow fissures formed by the glacier's movement over uneven ground. The guides showed us how to climb walls using just picks and crampons. The going was relatively easy, but you were always aware that you were on a block of ice several hundred metres thick, and occasional rumbles were a reminder of nature's unpredictable volatility.
We ate lunch beside a sapphire-coloured lake in the middle of an icy valley, and then it was time to look for a way off the glacier. This was the trickiest part of the trek, as much of the glacier is edged by sheer, high walls.
After all that ice, it was time for a meltdown. I was staying at Los Sauces, an estancia-style hotel in El Calafate. My room was warm and snug, with a tiny coffee machine and a vast, 10-pillow bed. At its restaurant I indulged in Patagonian specialities: spider crab, smoked salmon, cold cuts of wild boar and venison, and (most importantly of all) Patagonian lamb. Why animals raised in such extreme topographies should be so tender and tasty I cannot begin to guess, but the lamb's meat at Los Sauces was like brown butter.
My last stop presented several opportunities to burn it all off. It was the tiny village of El Chalt*, 110km north of El Calafate as the crow flies, but twice that by road. El Chalt* sits cosily in the narrow, grassy valley of the Río de las Vueltas ("winding river") and is Argentina's official "national trekking capital". It was founded only in 1985, and has an attractive frontier feel: all wood cabins, caravans and muddy roads. Raise your eyes, though, and you ogle the summits of a chain of spiky Andean peaks, the most impressive of which are Mount Fitz Roy, Mount Torre and Mount Saint-Exupry. Almost all the time clouds swirl around the mountains; the natives of the region, the Tehuelche, thought they were volcanoes. Wherever you go around El Chalt*, these mighty mountains, alongside dozens of lesser pinnacles, glacier-capped peaks and hard rock walls, dominate the vista.
Naturally, you want to get closer. The next morning I set off with Pablo to climb up to the Laguna de los Tres, a small lake in the glacial bowl at the foot of Fitz Roy's east face. At first, we were mainly walking in forests and across meadowlands, but after three hours we came to a tough-looking final incline leading to a ridge. We sweated and panted our way to the top, gradually becoming aware that the weather was worsening, and fast.
By the time we made the final few furlongs to the ridge from where, we'd been advised, we'd get the definitive iconic view of Mount Fitz Roy a full-scale snowstorm had descended. On arrival I could see the laguna, but between me and the mountain was a wall of pure white. It was a reminder that Patagonia, for all its pretty flowers and smart lodges, is, in meteorological terms, a suburb of Antarctica. When the weather closes in, you are not talking slight sleet or patchy showers.
We descended, slowly, and were soon away from the worst of the snow. Following a slightly different path, we crossed bizarre tree graveyards where bleached, bone-like branches were strewn across what looked like inland beaches. I thought there'd been a forest fire, but it was just that things take a long time to decompose in dry, windy Patagonia.
I paused for about half-an-hour, and a gigabyte of photographs, to observe a Magellanic woodpecker at work on a newly budding lenga tree. The gregarious bird, 30cm long with a striking vermilion head, hammers away with such vigour that the tree shakes as he tears off huge chunks of bark. He chatters loudly as he grafts, and walks upside down on the branches. But Pablo explained that his ultimate party trick is invisible: for the vibrations in the woodpecker's skull are so powerful that he wraps his long tongue round the back of his brain as a shock absorber.
That evening, the weather took a turn for the worse. But we were in another five-star lodge (even little El Chalt* has its luxuries) and it was actually a joy to be compelled to sit still, and eat and drink lavishly. One of the dilemmas of active tourism is that you can have such a wonderful, adrenalin-fuelled time that you forget to look around you. From sense-less cycling to crampon concentration to steep, snow-blind climbing, you could miss the fact that Patagonia is a sublime place just to look at. Through the big, double-glazed windows I watched the river valley turn white and leafed through books about Fitz Roy, Moreno and Magellan which also helped to put my adventures in context.
Then, finally, as we left El Chalt*, the storm blew all the clouds away and I got that ultimate, iconic view of the Fitz Roy massif against an impossibly clear, cobalt sky.
The writer travelled with Journey Latin America (020-8747 8315; www.journeylatinamerica.co.uk), which offers nine-day itineraries in Buenos Aires and Patagonia from 1,980 per person. This includes three nights at the Casa Los Sauces in Calafate, two nights at Los Cerros in El Chalt*, three nights at the Esplendor Palermo Hotel in Buenos Aires, excursions with guides, transfers and most meals. International flights to Argentina can be arranged by JLA from around 630 return.
Buenos Aires is served by British Airways (0870 850 9850; www.ba.com) from Heathrow, with an en-route stop in Sao Paulo, Brazil. Connecting flights from the UK are available with airlines such as Iberia (0870 609 0500; www.ibera.com) via Madrid, Lufthansa (0871 945 9747; www.lufthansa.co.uk) via Frankfurt and Air France (0870 142 4343; www.airfrance.co.uk) via Paris. Aerolineas Argentinas (020-7290 7887; www.aerolineas.com) flies from Gatwick via Madrid; the Gatwick-Madrid leg is operated by Air Comet Plus.
Parque Nacional Los Glaciares, Torres del Paine, Argentina (00 54 2902 491 005; www.losglaciares.com).
Argentina Tourism: www.turismo.gov.ar
LATA (Latin American Travel Association): 020-8715 2913; www.lata.org