My God Bolivia is cold. To be fair it's only the western half that suffers from a chronic lack of temperature but for some utterly unfathomable reason it's where 90% of the people choose to live. Arriving in La Paz, from Peru, is like glancing down into a huge crystal garden (the kind you could buy 20 years ago to experience the wonder of chemistry in the comfort of your own home). Shiny office blocks rise up from a chiselled canyon floor, the valley sides buttressed by pastel coloured spurs and crags. Overshadowing all and lending extra depth is the powder white backdrop of the Cordillera Real.

Most of La Paz proper runs along what must once have been a river bed, but money also flows with gravity and the poorest face the prospect of a daily lung-busting walk to and from their adobe homes on the vertiginous slopes. At nearly 4km above sea level, just standing up too quickly left me wheeling around like some wheezy old soak, gasping and blinking at all the funny coloured dots in front of my eyes.

But what the hell, I'm not here to relax. I paid good money to experience the extremes of physical discomfort, so it seemed only natural to want to go higher. Having missed out on two other peaks (Cotopaxi in Ecuador, and El Misti in Peru) this was possibly the last opportunity to scale a technically easy mountain. Huayna Potosi is 6,088m or an agonising 32ft short of the big 20k. It looks a lot more menacing that the other two perfect cones, but is considered relatively straightforward for those with no previous experience.

Unfortunately, the agency didn't specify "those with no previous experience and food poisoning." Having been ferried to base camp at 4,700m, introduced to the grinning guide, who was clearly suffering from severe sleep deprivation, and set off on the initial trek to the overnight camp at 5,200m, that's when it all started to go wrong.

It was bad enough carrying a tent, sleeping bag, mat, clothes, crampons, ice pick, poles, 4 litres of water and food, but being forced off a narrow icy path into waist deep snow to answer the increasingly frantic call of nature started chipping away at my resolve. I finally made it after 3 hours of pain and ignominy having suffered the slow procession of victorious climbers returning from the summit while squatting in a make shift ig-loo ("Buenos dias" you b-stards!)

Camp was little better. It was cold, it snowed and I'd lost my appetite so what little strength I had went on fending off frost bite. The other climbers were a jovial Frenchman, Benoit, who I'll have to be nice about as he bought me large quantities of Scotch once we got back to La Paz, and a lanky coca-chewing German, Daniel, who I don't have to be nice about because he bought me nothing. And is German. Plus every time he opened his mouth it looked like he'd swallowed a privet hedge. They were clearly far more experienced than me as they used phrases like 'double belay' and '60 degree traverse' and had an impressive array of sharp metal implements.

Anyway, to cut a long and shameful story short, we all set off at 1am, exactly the time when a huge icy mountain is at its most terrifying. Having not eaten that day and being utterly drained I would have struggled to climb into a bunk bed. So after one and a half hours of ascent and having crossed a number of yawning crevasses gaping like frozen Venus fly-traps, I called it a day and tried to collapse, only I couldn't because my crampons were firmly embedded in the glacier. Instead I toppled forward bending at the waist, and remained curled like a croquet hoop until the safety rope snapped tight and the others realised I was done. I spent the rest of night shivering in the tent like Scott, while the Franco-German Amundsen party cruised to the summit and back down in time for breakfast.

I did however get to see the sunrise over the vastness of the rainforest and the chain of Andean peaks stretching for hundreds of miles both north and south. I wont forget that in a hurry.

Chastened and sobered by the natural world, it was time to leave La Paz for the slightly warmer climes of Cochabamba, capitol of Bolivia's coca/cocaine trade. Not much to recommend there I'm afraid, but quite amusing to watch lots of little, shifty-looking planes fly in and out while policemen sit on their backsides cleaning their guns.

Onto Sucre which is home to the world's largest collection of fossilised dinosaur footprints. Hurtling back millions of years, the probable lives of these magnificent beasts are beautifully, and tastefully reconstructed with a bunch of plastic toys in a little sand pit. "You like me explain in English?" said the woman providing a commentary. "No gracias." You already lost most of your dignity when the leg fell off the Glyptodon.

From Sucre the increasingly rustic 'road' runs eastwards to Potosi, highest city in the world, and source of virtually all of colonial Spain's silver. One mountain (Cerro Rico) has provided four hundred years of dinner party cutlery and been the death of an estimated 6 million miners. Today, groups of men still comb the increasingly unstable hillsides for scraps of tin and silver. They have a career expectancy of just 10 years before they expire of silicosis pneumonia.

From Potosi to Uyuni, dusty and remote gateway to Bolivia's crown jewels - the world's largest salt lake and the awesome landscape of the Parque Nacional de Eduardo Avaroa. Standing in the middle of 12,000 square kms of perfectly flat salt is a dazzling experience. There is no sense of direction (many people have died trying to traverse the salt pan without a guide) and distance is impossible to judge - mountains that appear close are often over 100km away. Further into the park are vivid red, green, blue and yellow lakes, flecked with flamingos and ringed by volcanoes. It is an astonishing lunar environment and I feel privileged to have witnessed it (despite the -20 degree temperature).

After three days, the road jumps rather suddenly into Chile and the Atacama desert. Despite the very clear instructions not to bring any food or vegetation into the country, two Dutch girls sitting next to me on the bus had somehow forgotten that they were carrying a large bag of coca leaves, various salad items and a whole roast chicken. Oh what an amusing scene in customs. The poor Japanese guy who had neglected to obtain the necessary visa and was sent packing back to Uyuni (a bloody long way), was less amused.

So, having spent precisely 3 days in Chile (I will be back), it was on to Argentina. Salta, in the north east was the scene of my first shock. I stood transfixed in the aisle of the supermarket (called Disco) and stared at the prices. Argentina is a notoriously expensive country, but with an exchange rate that has devalued the currency by over 80%, things like beer, wine and steak (i.e. the important things) are now mind-bendingly cheap. Oh joy. My second shock was, having rented a car with some companions and driven into the wilderness, we stopped at a little village school in the middle of nowhere to say hello and found that the children were currently studying the Falklands. Their teacher had the glint of jingoistic zeal in her eye, so when asked where I was from I mumbled 'nglnd' and beat a hasty retreat.

Funny place this. Watched a Beatles tribute band last night and as the clock wound on to 4am, and the night grew cold, outside on the windswept pavement a crowd of onlookers peeked in through the windows, and toothless old men danced like lunatics, pumping their fists in the air and screaming at passers by.

It will be one of the hardest acts of my life to tear myself away from this extremely hospitable country. But in less than two weeks I will be in Rio and I suspect that might be quite fun.