In Namadgi National Park, info and maps are at the visitor's centre.
It is standard to say ... firstly, have you checked out Johnny Boy's Walkabout Blog ...
http://jevans.pcug.org.au/ There are 580 walks (so far) on the blog.
Or, in the morning do the 3 kilometre, Shanahan's Mountain Walking Track off Boboyan Road. From the car park it is one kilometre to the edge the escarpment, then south along the escarpment for about 700-800m, on a faint track in places, then it is a kilometre back to the car park on a well defined track. It is a simple triangular shaped circuit. The track is relatively faint in places along the escarpment but not hard to stay on or find. A simple walk but with spectacular views.
Then take the short drive to Brayshaw's Hut still on the Boboyan Road. Do the 10 kilometre Settler's Walk in the afternoon. You will see three restored High Country huts. There is good water at each of the huts, in tanks. These two walks are in the Southern ACT.
If you like climbing on tracks, perhaps take the track to the summit of Mount Tennent. This track starts at the visitor's centre and is part of the Australian Alps Walking Track. This is a cool walk when the climbing starts.
Warren.