It's been a while but Vietnam is awesome, varied, and super easy to travel. Basically one highway runs up and down the country, and you just ride it at your leisure.
Down south you have Saigin / Ho Chi Minh which is a crazy western /Asian fusion metropolis. Move up from there to the beach towns like Natrang, up towards the middle for some history (both the DMZ and the royal city of Hue), and then up to Hanoi which is this amazing throwback city, and then up and out to the eerie magic of Halong Bay and then up into the jungle mountains in the north (also part of the legendary Golden triangle).
Though tbh I would probably start up top with the jungle trekking and old country magic and then work my way down to the beaches and Saigpn at the end.