We actually did this trip in the reverse, coming from Hamilton to Dunkeld along the Glenelg Highway.
The scenery is wonderful! First of all, we passed by many paddocks full of either black Angus Cattle or hundreds of sheep grazing, then we started to see the Mountains.
Be prepared to pull off the road or stop at a pull off and take a photo or too, as there are good views of Mt. Sturgeon and Mt. Abrupt on the southern tip of the Grampians.
Bunjil's Shelter is one of Victoria's most important Aboriginal Art sites (The Grampians has the vast majority of them).
Bunjil (depicted in the painting) is the Great Ancestor spirit and creator in Aboriginal Mythology who created the people, law, and customs. He appears in many of the stories of the Dreamtime of the Koori people of south eastern Australia.
The dogs in the painting are Bunil's helpers.
The age of the painting is unknown. It was mentioned in European writings in 1884 when a local Aboriginal was questioned about the painting, and it was touched up in 1911 with European whitewash.
This area was once occupied by the Djab Wurrung tribe.
The setting for the art isn't fantastic, just a short, 5 minute, almost flat rocky walk from the carpark to where the rock overhang is, surrounded by fencing (there were some early attempts at grafitti at the site and so it's been fenced since the 1960s but at least you can manage to take photos ok without the grilles getting in the way. There is another walk you can take from the shelter though which is longer, if you want to explore the area a bit.
This is the only aboriginal art site in The Grampians where more than one colour has been used.
The shelter located just south of Stawell, about 10 kms off the main highway, so it's not a big detour to see it.
In the Grampians, you can go as little or as far off the beaten track as you like. There's just so many choices, and even though the park is so popular, I've never found it crowded, particularly on the longer walks.
Expect to see a lot of walkers on the Balconies and Pinnacle walks, and the ones more in the town.