Son La at the halfway point between Hanoi and Dien Bien Phu, the sleepy provincial capital of Son La was once the site of a sizeable French garrison during the French war, but today, aside from the ruins of the prison, the only evidence the French ever made it here is the baguettes and rich strong coffee. A mid-sized town, the provincial capital is split in two by a small estuary, the fertile banks of which are given over to small-scale farming.
For a town of little note, really the only point of interest here is the ruins of the French prison, so most visitors give Son La a single night's stay before continuing on towards Dien Bien Phu or Hanoi.
Getting around Son La is quite easy. As you arrive from Hanoi you will go through a somewhat puzzling section of roads that are way wider than the traffic flow currently demands. The road into town swells abruptly from one lane in either direction to five lanes then, just as abruptly, it drops back to it's normal size.
You'd be right to think that the Vietnamese government has great plans in store for Son La. It's part of a planned trade corridor via the Tay Trung border into northern Laos. But here is where the good roads end for the time being. Every inch of the 170 km of Highway 6 between Son La and Dien Bien Phu is being torn up, re-cut, and relaid. It's a toilsome labour, as the road goes through countless narrow passes high in the mountains. It's a dastardly road to navigate on your own, and don't expect to get any sleep on the bus.
Highway 6 is called Truong Chinh in town, and Phuong Quyet Tam further out by the bus station. It veers sharply to the west as it hits the town centre, and it then called Dien Bien Phu where the French Prison is located. The road on the west side of the river is To Hieu, on the northern stretch of which you'll find 26/8 Street by the park, with access to the Lookout Point. On the east side, the road is Chu Van Thinh. They're connected via two bridges -- Cau Trang, on Dien Bien Phu, and Cau Day Vang a bit to the north. There's a small unnamed bridge further north. If you're looking for Nguyen Luong Bang, head to the Highway 6 roundabout, and it branches off to the east.