A waterfall that is accessible from the Great Ocean Road is Carisbrook Falls.
The walk to the falls is only about 300m from the carpark. It is a gentle uphill walk to a viewing platform that looks over the falls from the other side of a gully. There is no path access to the waterfalls from the viewing platform.
The walk could take as little as 5-10 minutes one way to the platform depending on fitness.
Something that isn't obvious from the platform is that there are actually numerous tiers above what you can see. If you can get your hands on a copy of Anthony Car's "Waterfalls of the Otway Ranges" book, you can check out photos of the other tiers but these would be an offtrack mission for experienced hikers only.