Werribee Gorge, and specifically Falcon's Lookout is a popular walking and climbing location close to Melbourne. I recently went back there for a day with some friends, we had an absolute blast. If you go in there with low expectations for rock quality, it's a great day out.
The walk in takes you though an interesting gulley/small canyon. I always enjoy the walk out because of this section, even though it's tiring at the end of the day.
Take care near the top of the cliff at Falcon's lookout because there is quite a bit of small loose rock that is easy to knock down onto climbers standing below.
You can find heaps of great info and topos on Chockstone and TheCrag .