Vietnam's National Road 1A, from Da Nang City to Hue City in Central Vietnam.
The road goes over the Hai Van Pass, with beautiful views of Da Nang City, the coastline, Monkey Mountain and the mountains which the road traverses. After Lang Co, the road travels through several small villages, and two more smaller mountain passes. On the way, before entering Hue City, there is Bach Ma national park and rice fields, which seem to capture the iconic image of Vietnam. Once you arrive in Hue City, there is the usual Vietnam traffic and hustle and bustle of the city, with great historical sites from the original dynasties, the Cham people and the recent Vietnam War sites.
The mountain passes are very curvy, with some of my favorite turns in the world, with some parts of the highway being straight and flat. There are quite a few potholes to be aware of, but the road seems to be in decent condition, compared to other roads in Vietnam. The major issue is traffic, especially on blind curves, where busses and trucks pass eachother.
There aren't too many tourist attractions on the way, besides Bach Ma National park, the citadel on the Hai Van Pass and a few memorials along the way. In terms of American style rest stops, good luck. There are local markets, small coffee shops and other local outlets, but nothing big or advertised. There are plenty of gas stations, but that's about all they sell, is gas.
Motorcycle Road Additional info
The traffic is the main concern for drivers with little or no experience on the roads of Vietnam. It can be extremely dangerous, but if you know how the roads work, then you should be fine. Another issue of concern is, if you have a unique bike, or one that's imported, you could run into trouble if you have a flat or other mechanical issues.