This is the sign which I think Jonnosan describes
http://wildwalks.com/i.html?image_id=319181Here are the Wildwalk notes that take you from that sign at Lower Linda Falls to the clearing (note that this is not from the actual picnic area)
"From the intersection, this walk follows the faint track that heads directly away from the waterfall and away from the main track from behind the 'Federal Pass' sign. The track leads around the side of the hill (keeping the valley to your right) for about 60m, where this track steps down to join a wider track. Here the walk turns sharp right, and heads downhill for about 20m (noticing a nice cascade to your left), passing a couple of concrete pipe maintenance holes and then crossing a small creek (just downstream of an old timber bridge). The track bends left, leading down through the more open forest for about 200m, to go under a fallen tree and past a metal vent post (on your left). Here the track bends right to cross a small gully, then follows the now wider track as it leads downhill through the fairly moist forest and after about 240m, the ferns suddenly give way to a large clearing. Just past where the track opens up, there is a small campfire scar, and a large re-vegetating site from the old sewage treatment plant (on your right)."
There are otherways down as well, but this is one actually takes you via the clearing.
Hopefully you can piece it together now.
Matt