This is a five-night return walk into one of the deepest rainforest gorges in The Budawangs. From the Nerriga entrance (details here) the route follows the Redground Track and Endrick River Firetrail to the Folly Point turnoff, then along a foot track through dense Banksia and Hakea scrub. From Folly Point at elevation 700m there's what can best be described as a "negotiable route" that plunges to Camping Rock Creek in Hollands Gorge at 100m.
The Redground Track and the Endrick River Firetrail provide easy walking up to the Folly Point turnoff. There's actually a fairly popular cycling route that follows them through to Sassafras. The Folly Point foot track is reasonably well defined, but narrow, undulating, winding and partly overgrown with Banksia and Hakea bushes. You'll spend a fair bit of time ducking under overhanging branches and avoiding the encroaching spiky vegetation.
It's worth making the detour to Folly Point lookout for some of the best views in The Budawangs. This side trip to the west can be seen on the map above.
For the section from Folly Point down through Watsons Pass to Hollands Gorge you will need good off-track navigation skills, and some pack-hauling and chimneying up and down rock ledges is required. There are some metal spikes driven into the rock at the top of Watsons Pass that help with the first clamber, but after that you'll find there are a few places where you need to take your pack off to make progress. You might want to bring a pack-hauling rope.
The route down Watsons Pass heads steeply down to a cave (more of an overhang really) at around 400m elevation. The way is marked by cairns to some degree, but they peter out after the gully below the cave.There's a fair amount of fallen timber that complicates navigation and has presumably disturbed some of the cairns too. All vestiges of a track disappear soon after leaving the cave. I did this walk a few times in the 1990s and I remember a reasonably well defined track all the way down, but that's gone now.
From the cave the general idea is to aim for the spur that runs west from Castle Head (Corang 484948). Cross the gully below the cave, following the cairns, then head SSW, trending slightly downhill and aiming for the spur. The cairns become increasingly hard to find, but that route should keep you clear of the worst of the undergrowth. You'll cross a few small streamlines. Follow the spur down to Camping Rock Creek a few hundred metres or so upstream from the Hollands Creek junction. Don't descend too quickly before reaching the flank of the spur or you'll find your way hampered by lawyer vine and other undergrowth.
This walk is mostly on the Endrick 1:25000 topo map, with the Hollands Gorge section on the NE corner of Corang 1:25000. You can download PDFs here. It's probably worth bringing a GPS if you have one. From the map page you can download a KML file of the route. The off-track section from Folly Point to Hollands Gorge is derived from a GPS track of the return journey up the hill, so it might help to load that section into your GPS. Make sure you can still navigate when your GPS fails though, so bring a compass and printed maps and make sure you know how to use them. Bring a PLB on this walk: this is some of the most remote and inaccessible country in Morton National Park.
There are several decent campsites along the way. There's a top-notch one just after the second Endrick River crossing, which is conveniently located for a post-lunch start from the Nerriga entrance. Further along past the Styles Creek turnoff and The Vines is the Camp Rock campsite which could be reached in a day from the Nerriga entrance. Beyond that is the Folly Point campsite and the final campsite in Hollands Gorge. In an emergency there's also the cave on Watsons Pass about half-way down the descent from Folly Point. The Folly Point campsite can probably accommodate five or six tents.
Dave Singleton and I did this walk in November 2019 after a dry winter and spring and found sufficient water at all those campsites. At Camp Rock (Newhaven Gap area) and Folly Point the flow was pretty meagre, but both the Endrick River and Camping Rock Creek in Hollands Gorge were flowing well. We also crossed a small flowing stream between the Watsons Pass cave and Hollands Gorge. If you go in a particularly dry time, be prepared to continue on past Folly Point if there's no water there. At a guess I'd say if there's no flowing water at all in the creek near Camp Rock, your chances of finding flowing water at Folly Point may also be slim. At Folly Point there's a deep plunge pool which might never dry up, but given its location downstream from the campsite I'd only use that in an emergency after treating it.
It's probably possible to extend this walk into a loop, following Hollands Creek upstream, then up a spur to Mt Tran, around the base of Mt Haughton and back to Endrick River Firetrail via Styles Creek. I did this a couple of times in the 1990s and recall it was quite a slog. I suspect that this route is not as popular as it was when there was vehicle access all the way to Newhaven Gap, so I would expect progress along Hollands Gorge to be at least as slow as it was back then. In Bushwalking in The Budawangs, Ron Doughton also describes a route through to Monolith Valley.
The other variation on this walk would be to start and end at Sassafras, but my memory of the section from the Sassafras entrance to the Folly Point turnoff is that it's a fairly tedious bit of road.
Many thanks to Dave for his superior navigation skills!