Quoting this, found on Mrs Google: (tnx Robert)

“At 1,167 metres, Mount William (Duwul) is the highest point in the Grampians (Gariwerd) National Park and provides great 360-degree views of mountain ranges and open plains.

From the Mount William car park it takes a moderately fit person approximately 45 mins to walk to the summit. Despite the steep walk the great views make it a must see for anyone wanting to see the entire Grampians from one lookout. It’s a two kilometre walk each way from the car park.”

We can also visit the Halls Gap Ice Cream Shop, perhaps on the way back.”