Sleeper trains are one of the cheap, interesting ways to get around Vietnam. I had read a lot of horror stories about them being dirty and disgusting but my experience was that they were certainly noisy and bumpy, but clean and safe. However some other people in the next carriage had a major cock roach infestation to the point they couldn’t sleep, so I guess there is an element of luck in which carriage you get!
We got on the train at around 3pm so we saw quite a bit of the countryside as the sun was setting. Each carriage has 2 bunk beds, which I forgot to get a photo of.. But you get clean sheets and a thin mattress and air conditioning which sometime works so well you are freezing cold, and sometimes doesn’t work at all..
I opened one of the windows to watch the countryside pass, the trains don’t move particularly fast, but often posts or trees would be very close to the train so the occasional duck back inside the carriage was needed.