In Argentina , I recommend you in SALTA (north of the country)the "Train of the Clouds".
This is one of the three highest railroads in the world. It seems to be hanging from the giddy mountains, the visitor feels as if he were hanging from the clouds (that's the reason of the name)
No intent to criticise your country in any way, tiinchoo, but I found el tren de las nubes a bit of a tourist trap. Sure, the views are nice, but it's a slightly boring ride, too expensive to my taste. Unless you're a train buff, I wouldn't recommend it.
Best advice I can give you is to try and do your own trip. As invaluable as other ppl's information was to me before my own trip, there was one person who sticks out the most as provding the most sound advice to me from TP (shall remain nameless ) and that was exactly that - do it YOUR way. The thing about websites is that there are a lot of ppl just trying to up their numbers of posts, and in so doing, appear as if they are experts. No-one was more apprehensive than I was starting off on my adventures, and I have surprised even myself! Go out there and do it! You will be amazed at what you will figure out on your own - advice and tips are certainly helpful and will take you a long way, but they are nothing compared to what you can achieve yourself...and that is the best experience of all.
Have a basic route in mind, dont worry too much about pre-organising tours (they are easily done on the road), have a healthy bank balance, a good attitude...and go for it! You wont be sorry.