The train to Tucuman
However, I had heard that since the government had taken over the train system the trains had been upgraded and were a much more comfortable (and cheaper) option for the very long 26 hour journey from Buenos Aires to San Miguel de Tucuman.
Unfortunately, actually obtaining a ticket is unnecessarily complicated. You can only purchase tickets in the month of your departure despite the fact that if you want to book a private room, you must book very early and you can only purchase a ticket at one of the train stations in person and in cash.
Despite these difficulties I was able to obtain a ticket. I booked a camarote (private room) for $ARS1295 (around $A117). These are exceptional value for two people, however, for one they're around the same price as the bus.
There is also a dining car available for purchasing food.
The comedor (dining car)
Roast chicken - it was pretty tasty
The train leaves Retiro Station in Buenos Aires on Fridays and Mondays and heads North to its first stop at the city of Rosario.
Andean Condor in a tree
Cows near the river
San Antonio de Arroyos
Sun behind trees
Passing where the station used to be
San Miguel de Tucuman station