As an overview the route consists of spending roughly 1 hour going from Olbia to Nuoro and then 1 hour going from Nuoro to Lanusei. The last 15 minutes is the descent from Lanusei to
the valley of Pelau
The map on Google is fairly accurate until Lanusei but then I had some issues getting it to follow the correct route!
After leaving the airport simply follow signs to Nuoro. You will never actually go into Nuoro but will hit the ring road and there are 2 turns here in a short space of time so this is the main place to be careful.
When you start on the SS389 and follow signs to Lanusei this will last for the best part of an hour. There are a few bends for the last 15 minutes of this hour.
When you hit Lanusei it is probably easiest to drive through the village and as you come out there will be a large fork in the road with a road curving upwards to the right - see photo below.
This is signposted Cagliari, Loceri and SS125 and is the correct road to follow. This is different to that shown on the link but will be quicker - it is equivalent to going straight from marker D to marker E. In the worst case if you end up on the wrong road - to either Cardedu or Barisardo then it will not waste a huge amount of time. Follow this road for approx 10 minutes going downhill and you should come to the junction mentioned in E where you have to turn right and proceed over the bridge