By Deborah Bonello
Now, more than 50 years after that trip, Carlos Ferrer, known by his friends as Calica, has written a book, From Ernesto to Che, about their experiences.
That trip saw the transformation of his young childhood friend to the famous Che, the iconic figure known around the world.
Mr Ferrer, now 76 and living in Buenos Aires, explains why, after all this time, he decided to write the book.
"Before, I was very scared that whatever I said could be misunderstood," he says.
"But now that he's such important figure known around the world, I think that would be unlikely to happen.
"I felt obliged to tell the part of the story that I had the honour to share with Ernesto Guevara."
Mr Ferrer has also shared his story with actor Benicio del Toro, who is playing Guevara in a new film being directed by Steven Soderbergh.
"I don't call him Che - Che is what a lot of people call him - but my friend is called Ernesto, or Ernestito. But when I was angry with him, I'd call him something else, but I can't say it here," Mr Ferrer says.
Ernesto, he says in his book, was always demanding.
"When we were 11-years-old, after some typical argument of ours, he came to confront me with his gang, of which of course he was the leader.
"'Look,' he said to me, 'if you want to get back into the gang you have to demonstrate your courage.'
"I didn't want to be on the outside, so accepted and they took me to a place where there was a huge rock with a tunnel underneath. 'If you cross the tunnel, you'll be back in the gang,' he said.
"Without thinking twice, I set to making it through the tunnel, body to ground, although I was terrified that a snake or a spider would bite me at any moment, that a frog would jump on me or I would be crushed by a landslide.
"It seemed like 100 years, but finally I reached the other side and everybody congratulated me. My title of friend of Ernesto had been reclaimed," he recalls.
Carlos Ferrer and Che Guevara travelled through Peru, Bolivia and finally Ecuador, where they went their separate ways. Che continued to Mexico, where his first meeting with Fidel Castro took place.
The two friends arrived in Bolivia just when the National Revolutionary Movement was in the process of overthrowing the military regime there.
"Ernesto had already seen in his first trip [with Alberto Granada, subject of the film The Motorcycle Diaries] the harsh miseries, the lack of medicine, education and culture, the lack of attention to those countries," says Carlos Ferrer.
At the time, much of Latin America was in the grip of dictators and the second trip helped awaken the revolutionary in Guevara, he says.
"If he needed to know anything else about how people in these towns were living, this was a great way to do it. We had the opportunity to see how the miners were treated - Bolivians and miners were treated like animals," says Carlos Ferrer.
If Guevara had not been killed in Bolivia in 1967, Mr Ferrer thinks he would have gone on to great things.
"I think he would be an important political leader now," he says.