I would really like to once ride with the [tren a las Nubes](http://en.wikipedia.org/wiki/Tren_a_las_Nubes). Wikipedia says the tour takes 15 hours, but I can't find any information on where to buy tickets and if reservation is necessary. And how much does it cost?

The highest point on the route is over 4200 meters. Do I need to take any special precautions because of this height? Normally if I go climbing in the Alps it is necessary to prepare when going above 4000 meters. But in this case, it is only a passive activity and most important only for a short period. I think you can only get really altitude sick after approximately 6 hours. So it shouldn't be a problem in this case?