Total distance for out and back was 9 km with minimal climb.
Start the walk at Port Istana. There is a large free car park just before the turning circle at the end of the road. From there just head down to beach and turn right along the beach and then follow the paths generally keeping very close to the shore.
Some lovely views:
After the first beach there is a section of fairly narrow path with a sharp drop of a few metres into the sea to your left. In places the path disappears and requires a small step over the difficult section. Whilst not particularly difficult it may not be suitable for children or the less stable on feet.
This first section is the hardest bit and thereafter paths are something like the picture below.
In October Porto San Paolo was almost dead. After a bit of looking we found a hotel (Hotel Castello di Tavolara) open for coffee and croissant where we stopped for 30 minutes before heading back the way we came.