Train travel in Vietnam is pretty straightforward as there’s only one line between Saigon in the south and Hanoi in the north. Traveling the whole length of the Reunification Line would take a time-effective two nights and one day, in a comfortable soft sleeper coupe. The only thing stressful about it is buying the tickets in the huge ticketing hall of Saigon Station, where little English is spoken and queues are long.
Our plan was to transit through Vietnam rather quickly, but we did split up the long journey by stopping over in Phan Thiet and Hoi An for a few days. The most time, however, we spent in Hanoi sorting out our Chinese visa. It took four visits to the embassy and a lot of waiting and improvising, but after five days we had our visas in hand and could finally buy our train tickets to Nanning. Interesting detail: in order to get a Chinese visa in Hanoi you must have a valid ticket to China, but to buy a train ticket to China you must have a Chinese visa (guess how we solved that one).