The petroglyphs that I saw at Volcanoes National Park were along the Chain of Craters Road. There was a small pullout to park the car and a simple walk in to see the petroglyphs. The map indicated that the trail was .7 miles, but since the terrain was mostly level, it was not a strenuous hike.
The trail is marked by cairns (small rock piles), and they lead to a wooden deck that encircles the petroglyphs. You can walk around on the deck and look over the rails to see the carvings. Since the petroglyphs are protected, it is important that people do not walk on or touch the carvings. The images were carved by the ancestors of some people who are still local to the area.
The image on the right shows many holes dug into the rock. The people placed the umbilical cord of a newborn into a hole carved into the rock. If left undiscovered, the child would not grow up into a thief. In this image, there are many holes, and one interesting one that is surrounded by three circles.