In Vietnam, some long journeys can be made by train, in particular: Hanoi - Lao Cai; Hanoi - Hue; Danang - Ho Chi Minh city.
With the exception of the Hanoi - Lao Cai route, we rarely or do not recommend the train. Indeed, on these other journeys, the train is slow (50 km per hour), noisy and uncomfortable. These are in addition to the night trains and it is difficult to sleep well.
Some tour operators can offer you the Hanoi - Hue train in order to reduce the cost of the trip. But if you can put in a little effort, we highly recommend flying to save time and avoid fatigue.
Specifically on the Hanoi - Lao Cai route: The train travels at an average speed of 60 km / hour, on rails 1.2 meters wide. It is therefore impossible to compare it to the TGV. However, you will travel in cabins with soft berths (small beds 80 centimeters wide) with air conditioning.