I did a grand tour today on whats known as the NSW coastline cycleway, Thirroul to Wollongong and back. This was a fantastic ride along the coast with loads and loads of things to stop and check out. Not the least of which is, the fantastic beaches. Really you need to spend a whole day here exploring this path to do it justice.
The trail runs north as far as Stanwell and as far south as Port Kembla. The northern sections do involve riding on a busy winding road, so not optimum family bike riding territory. I cannot speak for the path south to Port Kembla, but the terrain is flat and the distance is short, so it wouldn't add much to your journey.
Obviously you can start anywhere, but I would recommend starting North, head south, have lunch near Flagstaff hill and return.
This is about 16km of bike path making 32km return.
It is not really a loop ride, but it is worth riding both ways because it is so much fun. Almost flat- there is about 100m of steep uphill at Thirroul, but everything else is gentle inclines. I did it with the trailer, some sections can be a bit bumpy but not too bad.
Obviously you can start anywhere, but I would recommend starting North, head south, have lunch near Flagstaff hill and return. You will usually get a breeze behind you in the afternoon, but I did have the sun blasting straight into the trailer on the trip back (12-1pm), another hour of lounging at cafes or playing at the park would have fixed that.
Navigation is pretty straight forward, keep the sea on your left! There are a couple of spots you need to look for signs, but nothing very tricky.
Food and public amenities are plentiful each beach has playgrounds and toilets. The last section near the Wollongong harbour can be very crowded with walkers so take care.
If you needed to escape at any point, or simply ride one way, the train line is not too far inland. I cant comment on the regularity of trains on the weekends however.
If heading south and returning on the train to Thirroul, Wollongong train station is found by heading slightly south from the lighthouse around the stadium then inland 600m on Burelli st footpaths
[2017 Edit] I rode the final section from Wollongong harbour south to Port Kembla, and I wouldnt really recommend that unless you actually needed to go there. It runs as footpath along springhill road past the Port Kembla heavy industry. There is a small interesting section at the Port Kembla breakwater, but then its footpaths again continuing south. I got as far as the bridge at Windang, which is 20km south of Wollongong.