The largest river in northern Vietnam, the Red River, has its origins in the Yunnan province of China, and then runs southeast, eventually meeting the Gulf of Tonkin.
This is not an area of Vietnam easily explored and by far the best way is by river cruise, currently only offered by Pandaw Cruises.
This is a combination of scenic beauty, lively and interesting (sometimes industrial) life of the river and exploring rivers where no other river cruisers operate.
Sailing deep into Highland Vietnam you'll discover mountain villages and a number of tribal areas. The Pandaw Cruise goes as far as is navigable up the Song Red River and then down the little known Da or Black River.