DN66A is a very challenging road located in western Romania. The road is mostly gravel and links the towns of Petroșani and Tatu. The road is very rough--only try driving it in a 2wd car, if you're planning to buy a new car.
The road is mostly gravel. Expect holes of almost 50 cm deep, rock/trees fall, a very narrow road and there are some narrow sections -scarcely wide enough for two cars- where if two vehicles have to pass each other, one might have to reverse for some kilometers of winding narrow road to get to a place wide enough to pass.
One of the most challenging parts of the road is going along the Acumularea Cerna reservoir. Expect more than 100 turns in only 20km. Open to all motorized vehicles, however, strongly recommended for high clearance, 4-wheel drive vehicles.