From south VietNam to North VietNam, either by air or train. train will be much cheaper, even with foreigner price. serveral classes you can choose, from no A/C no paded seats to sleeping cabin with A/C of coarse. price vary from 15.00 to 50.00 foods included. from Saigon to Hanoi will take about 2 nights and 1 days, you will enjoy the differences as you pass by many region of VietNam, from high rise building to rice paddies to mountains. Halong Bay is one the most wonder nature in the world. can/t descript the beauty of it with words or pictures, a must see place before you pass away ;-)