I've done two 24 hour (one way) train journeys, they're fantastic. Paris to Lisbon (for honeymoon) changing trains to Iberian gauge at Irun/Hendaye. And Viedma to Bariloche with the desolation of the pampas and the stunning views as you approach the mountains. I've also done a 3 night 4 day ferry through the Chilean Fjords from Puerto Montt down to Puerto Natales (in order to go do the "W" in Torres del Paine). So much stunning scenery to look at (and a bar at night!).
Travelling in Argentina many people use coaches to go long distances between cities as air travel is so much more expensive. You can get a coach from Puerto Iguazu to Ushuaia if you've got a spare 60 odd hours. The coaches are surprisingly comfy with big reclining seats that are not far off being full beds. We mainly did 12-14h overnight trips between cities so we got some sleep and saved on a night's accommodation.