The airstrip ran north to south next to what is now Trafalgar Avenue, Woy Woy. It was constructed from compacted red gravel. The red gravel may still be seen (if you look hard enough) along the edge of the road surface in some places. As Trafalgar Avenue has a slight bend at the northern end it's unclear to me exactly what the alignment was, however it was of a substantial length roughly parallel with current day Trafalgar Ave.
The hangars and service area were located in what is now Alma Avenue. Some hangars or support may still be in existence, perhaps much modified, used as warehouses or other industrial buildings.
The airfield was last used in 1946 and officially closed by 1950; the land subsequently developed for residences. A last-ditch stand was made to preserve both this strip and Tuggerah to the north as emergency landing fields between Sydney and Brisbane but as the reliability of commercial aircraft improved the need for such airfields declined. An anti-aircraft battery protected the airfield, located in Blackwall Mountain Reserve to the north and east of the strip.
From time to time artifacts, including aero engines and drop tanks have been found discarded and buried alongside the strip. More details may be found on Steve's All things Woy blog and a reworded version with slight differences here and a crash landing in 1950.
Another post by me on this strip.
Want even more? Here is an updated list of Sydney's airports.