Just two kilometres past Da-Bia heading south, there's a well-marked turn that leads to Vung Ro Bay.
It's slated for resort development, but so far the funds for a forward push have remained illusive. There is an ambitious stretch of new road that has been built along the edge of the bay which terminates in the small town of Vung Ro and then peters out.
As you come down the harbour road from Highway 1A, the views are spectacular. Vung Ro is a deep-water port that has figured largely in the maritime history of Vietnam. The road eventually terminates in a pumping station, but to continue touring the bay, take a left just before the bridge just before the pier where the big ships are docked. It's a rough dirt road, but it eventually leads into town, where there are plenty of places to grab a bite or a beverage. From there, the road becomes quite good and continues north along the water, passing by some truly great isolated beaches, including Mui Dien Cape (also known as Dai Lanh Point) with a lighthouse overlooking the water next to a pristine, though shadeless, beach. This constitutes the easternmost point on mainland Vietnam.
It is not recommended that you try to return to Tuy Hoa via this road. It soon becomes a long, slow, tedious journey once the road leave the water, and there's no turnoff to take you west to hook up with Highway 1A. The best bet it to head back the way you came, or if you insist, head north and do what we did -- give up and head west along one of the narrow dirt paths through the rice-fields to find the main highway. Take it slow, follow the locals, and don't try it if you're on four wheels.