That sinkhole (and the entire area) is a crazy place. Really unusual landscape.
Some may be interested in this pic of the sinkhole/Lake Sydney outlet taken early last year.

- Lake Sydney outlet & Mt Bobs
Looking south towards Mt Bobs, with the main creek/outlet from Lake Sydney coming in from the right of the picture.
Also FYI, when I was there last year, the track was VERY overgrown after the turnoff from the Farmhouse Creek track, and the climb up to that knoll was definitely Moss Ridge-esque
There is a stunning (and a bit spooky) King Billy Pine forest towards the top of the ridge. Really dark and open understory here means care has to be taken to locate the next pink tape before moving in order not to lose the track. The pine fronds all over the ground mean no discernible tracks on the ground to follow.
The descent into Lake Sydney was much easier, but there was lots and lots of mud on the valley floor, and not much in the way of track marking. It becomes quite tricky to pick the best way forwards in places (ie. which of the manifold muddy bog holes is the actual track). Ended up being a fairly long and hard day just to get to the lake. Rain and sleet didn't help
I would like to go back, but - as someone else mentioned - probably best done with a friend or as a group (and not in the sleet).