2018 Update: We've been told via the comments that the bus we used may no longer be in operation or on limited days. Please keep this in mind when planning.
Direct travel from Hong Kong to Hanoi has been described as a headache for many travelers who have attempted the route without flying. Why is this a headache you might ask?
Well, according to train travel site Seat61, the shortest possible itinerary that includes train travel takes just over two days, a few connecting cities (there is no Hong Kong to Hanoi train directly), and nearly $100 USD of funds consumed in the process just for transportation alone.
However, in my planning I found another method that could quite possibly be the worlds shortest duration in traveling between Hong Kong and Hanoi, requiring just 23 hours from door to door and a grand total of roughly $60 USD.
Train travel on this particular route siphons you through multiple different cities, typically being Hong Kong/Shenzhen to Guangzhuo, onward to Nanning, and then finally to the border and down to Hanoi.
The problem with this is that one or more of the routes is often done by night train and produces an extra day of travel and an increased cost. However, there is one often overlooked option: a night bus.