Birrabang Brook is a nice creek, but has only a very small section of canyon. Nevertheless it gets a reasonable amount of visitors as it has no abseils and no swims, making for more of a bushwalk than a canyon.
Driving west along Bells Line of Road, park 1.3km past the Mt Wilson turnoff, where a couple of green posts block the start of an old fire trail. The trail is clear and easy to follow down the ridge. It begins to descend steeply toward the creek, and near the bottom it splits in two. The left path is better trodden, although it is a short abseil down a slippery rock, or a scramble around the left to get into the creek at MGA518852 (Mt Wilson). The canyon begins less than 200m downstream from here. Apparently the right path is an easier route (http://www.geocities.com/wcieslik/canyon28.htm) although I have not tried it.
The trip is relatively dry - with scrambling you can avoid getting wet much past your knees at normal water levels.
The creek is quite enclosed early on, with many overhangs. There are quite a number of shallow pools to be waded through. Some deeper pools emerge and there are a few required scrambles to avoid getting wet - one easy one up to the right above a waist deep pool, one harder one along the left for about 10m above a chest deep pool. Then a scramble up the left to avoid a 3m abseil. The abseil goes into the most canyon-like section - it is worth checking it out from below although it involves a swim to enjoy fully.
The rest is relatively straightforward, although occasional scrambling may be required.
The exit gully on the right at MGA508843 is fairly obvious as you can clearly see the sky up it. There is a faint track which leads up to the ridge, and from there you can follow the ridge back to the road and it is about 800m back to the car.