Rock Art of the Mediterranean Basin by Ilya Burlak
I only have a sample size of one, but I suspect that only a small portion of the locations that comprise this WHS offer any rock art that is worth the effort to see. The easy rule of thumb should be that if searching the internet does not yield explicit mention or photos of discernible rock art in a given location, it probably has little-to-none.
I went to see Pedra de les Orenetes because it is located not far from my recent base on Costa Brava. It turned out to be quite accessible: If you park in a dead end at the edge of Urb. La Pineda in El Bosc de Ruscalleda, it will take you only 15-20 minutes of walking on the relatively flat Ruta Prehistorica to reach Pedra.
Which turns out to be an expressive pile of rocks. If you are into rocks and hiking - great. If you are after prehistoric art - tough luck. All you will find is a couple of smudges that indicate where the drawings used to be. I allow that a recognition that an ancient human once drew on these rocks may be worthy of the WH inscription, but it's a stretch to count this location as an exhibit of the prehistoric art.
As is a stretch for me to count this WHS as visited. My personal definition of "visited" puts premium on the effort to see any inscribed component of a given site. The effort I made. But without actually seeing any rock art, I have to put an asterisk against this entry until I get an opportunity to see better preserved examples.