We set off in a convoy from Salta station in north-west Argentina dead on 7am to catch El Tren a Las Nubes, the Train to the Clouds. There are four coaches, a double-decker bus in case one of them conks out, a pick-up truck with a winch and loaded with spare tyres, and at the back, slightly worryingly, an ambulance.
For we’re heading 13,800ft or 4,220metres up into the Andes Mountains. And at that height, some passengers – despite following advice to drink coca tea and chew coca leaves like the Incas used to do – will invariably suffer altitude sickness.
It’s the third or maybe the fourth, fifth or even sixth – reports vary – the highest railway line in the world after one in Tibet and another in Peru. It does, though, have the world’s highest and most spectacular viaduct. And we are going to cross it – not once but twice.
The line was built during the early part of the last century, mainly to cart gold, silver, zinc and copper mined in the Andes all the way from Salta to Antofagasta, 270 miles away on the Pacific coast in Chile.
But over the years it has fallen into such disrepair that following avalanches and derailments – including one where people had to be rescued by helicopter – much of the route is now considered too dangerous for passenger trains.
That’s why we are making the first part of our journey by coach, before eventually clambering aboard the eight gleaming blue carriages which are waiting for us at the station in the little town of San Antonio de los Cobres.
At the front, coupled up to a hulking diesel locomotive with an extremely loud horn, is the buffet coach. At the back is the first aid car, equipped with oxygen and staffed by nurses and paramedics.
By the time the journey is finally over, they will have been busy. Altitude sickness can kick in at around 8,000ft and we’re going up to almost 14,000.
Most people will just find themselves a bit short of breath at that height, but others get dizzy, some vomit and a few feels quite ill. Luckily I just suffer a bit of a headache.
Everybody has an allocated seat and mine is next to a family from Buenos Aires, who don’t speak a word of English. My Spanish is rusty, but we smile and manage to strike up a conversation: about football, about Argentina, about Britain, about almost everything except the Falklands/Las Malvinas, which I suspect is probably best to avoid!
I offer them Trebor mints, which they politely refuse. In return, they offer me a delicious salami sandwich, which I greedily accept. And before we finally shake hands and part, they invite me to visit them the next time I am in the capital.
Like most Argentinians, they are immensely proud of this early railway ilne. And who can blame them as it traverses 21 tunnels, 29 bridges and 13 viaducts through stunning mountain scenery, passing a dormant volcano and rocks with dinosaur footprints, and skirting disused mine workings before finally reaching the magnificent Meccano-like La Polvarilla viaduct.
Partly designed by French engineer Gustave Eiffel, of Tower fame and held up on six 210ft tall pillars, it’s the highest railway bridge in the world, built on a 735ft long curve and with the track laid at a slight angle instead of being flat.
Our train trundles slowly over it as passengers lean out the windows taking photos and then stops before reversing back across and grinding to a halt. The Argentinians break into a spontaneous and loud round of applause as if it’s a miracle we didn’t all plunge to our deaths into the ravine below.
It’s the cue for everybody to pile off to take photographs of each other on a little grassy plateau area where local indigenous people are selling snacks, llama wool scarves, ponchos and various other souvenirs.
But before retracing our journey back through the mountains to San Antonio de los Cobres, the Argentinian passengers suddenly stand to attention and begin patriotically singing the national anthem as the country’s flag is run up solemnly to a flagpole.
It’s a nice touch, although somehow I can’t see it catching on at Euston every morning when the 7.01am from Manchester Piccadilly rolls in.
A first aid carriage with paramedics might be a good idea in Britain, however.
Just the job for treating passengers suffering from shock in the unlikely event that their train arrives on time!
For more details about El Tren a Las Nubes, and to book, visit trenalasnubes.com.ar/inicio-en
G-Adventures arrange various Argentina tours, including one taking travellers from Buenos Aires to Rio via the spectacular Iguazu Falls – see gadventures.co.uk/destinations/south-america/argentina