The Great Ocean Road is Australia's great coastal drive, running west from Torquay toward Allansford through surf beaches, rainforest, fishing towns, and the battered limestone cliffs of the Shipwreck Coast. It is famous for the Twelve Apostles, but the road is better when you treat them as the climax rather than the only reason to go.
Start with surf culture around Bells Beach and Torquay, then slow down through Lorne, Apollo Bay, and the wet green gullies of the Otways. The inland detours to Maits Rest, Hopetoun Falls, and the Redwoods of the Otway Ranges are what keep the trip from becoming one long procession of lookout stops.
You can do the road as a long day from Melbourne or Geelong, but that is the least satisfying version. Stay overnight if you can, because sunrise and sunset change the cliffs completely, and the tour-bus rhythm is much easier to dodge when you are already on the coast.