Be prepared to deal with huge amounts, not because Vietnam is expensive but because for most of the countries 1 Dong will be equal to several thousand unit of your currency. For instance 1€= 21.000 dong.

• TRAIN:
  
  
  • Check carefully on the net:
    - the Vietnamese railway website: https://vietnam-railway.com/
    - the worldwide trainschedules in http://www.seat61.com/Vietnam.htm#.VuZz0PkrLIU
    
    
    
  • Is it more convenient to fly or to take a train?
    If you compare from a cost/time benefit flying will turn out more convenient (ie: Danang- HoChimin by train 60$ in 15h, by flight 100$ in 15h).
    However from the travel standpoint taking the train you'll experience far more the country/people than on the flight, that's why I really reccomend to experience the train.
    
    
    
  • How long Hanoi- Ho Chi Minh takes?
    Assuming you want to do in just one shot it'll take 35-40h according to the trains you'll take
    
    
    
  • Which is the most unconvenient leg you did as concerns the schedule?
    While Hanoi to Danang is very conveninent having a train leaving Hanoi at 7.00 pm and arriving in Danang at 11.00am,
    I cannot say the same for the Danang- Ho Chi Minh leg since the trains leave late in the evening to arrive in the middle of the day.
    
    
  • How many trains are there?
    Be aware that most of the trains to the full leg Hanoi- HoChiminh, implying that:
    - if you need to do get on and get off in intermediate towns the timing might be unconvenient (ie: 4.00 am)
    - trains will be easily full even if the leg you are interested is not popular
    
    
    
    

  • Train classes:
    1) First class: 2 bed berth (Livingstone train)
    2) Soft bed: 4 bed berth
    3) Hard bed: 6 bed berth
    4) Hard seats
    

    The best bed is the lower one (also the most expensive)
    In the berth A/C is freezing so the best is to have a tape to close the A/C slots above your bed.
    On the train you won't find that much to eat so bring your own food
    About buying train tickets:
    I've never tried personally but I've read several complaints about people trying to buy them on line unsuccessfully. It seems the Vietnamese railway websites accept only Vietnamese credit cards.
    Once in Vietnam the options are the station or the travel agencies.
    If you are told by an agency that a train is fully booked try at least another one.
    NB: IF TRAVELLING IN HIGH SEASON BUY THE TICKET AT LEAST 6 DAYS IN ADVANCE
    
    
    

• How to reach Cat Ba Island from Hanoi?
  First of all DO NOT take the 15USD package offered by all the agencies and by the hotel in Hanoi!
  You'll find yourself on a bus for 3 hours to reach Haiphong than another 1 hour bus trip to get to an harbor placed in the middle of nothing. As third step on a shitty boat for another hour to arrive in a rundown dock, and finally again 1 hour by bus to be dropped in Cat Ba town. Much faster, cheaper and comfortable is the train that takes 2.5h from Hanoi to Haiphong; from here the speed boat that in 1h will bring you directly in the heart of Cat Ba city. (check the train latest schedule (Hanoi- Haiphong) in internet)
  
  
  
  
• General Tips:
  - If you decide to visit in the north of Vietnam in December and January be aware that it'll be cold and rainy. Bring the right outfit to cope with such weather.

  - In Vietnam there's a wide choice of night buses and in particular I got surprised by a VIP sleeping bus we took to reach the Can Tho from Saigon with a bed/seat layout I had never seen so far. Tilting seats that becomes beds set in a two deck lay out
  
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  The only downside is the Vietnamese length of such beds that won't make you enjoy it if you are taller than 160cm
  - Is it better Hanoi or Ho Chi Min?
  I far preferred Hanoi since more traditional than the cosmopolitan Ho Chi Min, but an expat will say exactly the opposite. In the capital you will find more highlights (Ho Chi Min museum and mausoleum, the water puppet show), while his southern counterpart more night life. The thumb rule is, as I read once, 'Hanoi is for the day, Ho Chi Min for the night'
  - About Ho Chi Min:
  Ho Chi Min mausoleum in Hanoi opens only in the morning till 10.45am
  Ho Chi Min museum (next to the mausoleum) is unremarkable unless you have a guide; you can hire one but only in the morning.
  - Don't miss the Caodaist temples: this is a sect merging several religions as Islam, Christian, Buddhism,.. and worshipping among others Shakespeare, Giovanna D'arco, Victor Hugo. The main temple is 2h from Ho Chi Min, but there are also others as the one in Danang. You can attend the prayer as I did and it's an interesting experience.