It is no longer possible to ride along the train line from Waterfall to Heathcote. To complete a loop of the Royal National Park crossing over and riding North inside Heathcote National Park seems a far better idea. The electricity management trail that runs south from Mirang firetrail is very rough in places and hasn't been graded in years.

To do a loop of the Heathcote NP, ride Mirang firetrail downhill for about 2.5km before joining the pipeline track. Following this south will eventually lead to the Woronora Dam Road. Turn right to go to the dam or turn left to head back to Waterfall.

A singletrack starts to the west of the industrial area at Heathcote.
It winds up and down the ridges before emerging halfway along the Mirange Firetrail.
From here head back towards the highway along Mirang and another singletrack starts on the right hand side. This is a very nice singletrack - a bit technical in places but flowy in others. There is quite a steep climb at the end just before it emerges on the Abaroo Creek firetrail. There is quite a steep climb up this firetrail for about 500m. About 3/4 of the way up there is a small trail on the RH side which leads to some aboriginal rock carvings.

The Abaroo firetrail then joins the Sebasterpol firetrail that leads back to the highway or the electricity management trail.