Rode this route in September 2017 from north to south. The ascent to the plateau was fabulous riding with lots of interesting corners and 180 degree corners and great views. The ride across the plateau was very pleasant with lots of animals (some of them on the road). Then the descent from the south end of the park and down into Estella was a different type of scenery altogether. There was very little traffic on the road in any of the sections.
I have two videos of the route -
This road crosses Urbasa Park. The road is narrow, with good corners, some tourists, some cows shits and outstanding views. Not for speeding.