We return the car to Salta hassle-free. Next morning an excursion to the northwestern tip of Argentina, our guide the husband of the city tour guide. They take it in turns to stay home with the baby. The car the same too, easily recognisable by the long crack snaking along the windscreen, thankfully below the driver's line of vision. I think of UK ads for urgent repairs to chips, but this is a veteran crack and resists a day of bouncing in a non 4x4 on unmade roads.

We travel with a couple of amiable Canadian dairy farmers whose daughter is considering a university elective in Brighton as she plays rugby, half way round the world we learn we have a women's rugby team. I am sandwiched in the back between the men for two days, ascending firstly alongside the route of the famed and aptly named Train of the Clouds, now sadly only running once a week in the high season, so many fewer visitors here than south in Patagonia. A new highway is being built and the railway bridges look rickety and rusty so its days may be numbered.

The vast pure white salt flats of Salinas Grande are blinding, mineral salts from long dead volcanoes left as the lake evaporates. Long narrow trenches scooped out a foot or two deep until water is reached, the salt taken for processing, evaporation renewing the salt crust. The water is clear, blue and feels soapy, it contains a lot of borax. Men are bussed to work a fortnight shift far from home, supplementing their pay selling souvenirs and charging tourists 5 pesos (30p) to use a chemical toilet raised up on a heap of salt, leaning forward, latchless door swinging open. You really need a friend. There are no bushes or trees for miles.

4170m our highest point, we move slowly as advised, drink a lot of water and are fine, maybe breathing harder uphill and slightly sluggish and muzzy-headed at most, by evening a slight headache. The guide chews coca leaves constantly, claiming it is just a local custom, not addictive, popping ever more small bay-like leaves into his cheek, his chewing and sucking fills the car with a faint odour of mouldy green tea. Reluctantly he gives us a few to try, not unpleasant, do I imagine a clearer head, brighter colours? I buy a box of coca tea bags and coca sweets from an old woman in the square at San Antonio to investigate further.