The tunnel forms a complete underground system from North Head, near Manly, to the Lane Cove overflow site on the western side of the Lane Cove River.
There is a junction at Tunks Park, 9.5 km west of North Head. From this junction, a 3.7 km, branch tunnel Help Descriptionruns to Scotts Creek near Castle Cove.
There are also large underground caverns at North Head and Tunks Park. They were originally built to park tunnel boring machines, store equipment or as underground workshops. They are now used for ventilation. - "Sydney Water"
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