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.
I did a 24 hour rail trip from Narvik, Norway to Gothenburg, Sweden. We changed trains in Boden, Sweden. It was ... long. The first few hours, over the mountains, was fantastic. Once we passed Kiruna it was forest. Lots and lots of forest. This was in summer, and there was overcast light almost the entire time. There was no feeling of progress during the journey.
Yeah, waking up at dawn on a coach in the middle of the Pampa is a great experience. The front seats on the upper floor have a stunning cockpit view. I've done it on the trip from Bariloche to Buenos Aires and from Buenos Aires to Tilcara, and it's well worth the sore legs you'll get for sitting all that time.
Try the Amritsar to New Dehli overnight. For the real experience, try second class, where my friend and I shared a small cubby with a family of five (all flights cancelled for weather, no first class left).
That'll make you appreciate the Shinkansen or ICE networks.
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.