Vietnam's air-conditioned trains are safe, comfortable & inexpensive, the ideal way for independent travellers to get around and see Vietnam at ground level. The train journeys are an experience in themselves and become an integral part of your visit to Vietnam. You might even meet some Vietnamese people.
Inexperienced travellers often mistakenly think they'll save time by using internal flights - in fact, an overnight train ride from Hanoi to Hué or Danang is not only far more of an experience (and cheaper) than a flight, the train actually saves time compared to flying, because the train leaves Hanoi city centre in the evening and arrives in Hué city centre next morning.
Flying takes 4 or 5 hours out of your sightseeing day in getting to a remote airport, checking in, taking the flight itself, collecting your bags and getting back into the city centre. And the sleeper trains saves a hotel bill, too. Air-conditioned trains with sleepers and on-board catering link Hanoi, Hué, Danang, Nha Trang, and Saigon (Ho Chi Minh City). Hoi An has no station, but it's just 30km by bus or taxi from Danang. Overnight train travel from Hanoi to Lao Cai and by road to Sapa is the best option.