This is a "Southern Old Lady" or "Granny" moth. Apparently they are hosted on Acacias. This one was on the wall of the recently refurbished Blackwood public dunnies. There used to be a couple of Flinders Ranges wattles (Acacia iteaphylla) next to the toilets on Australia Post land but they cut them down so this moth is probably wondering what happened to its habitat!
Incidentally the refurbished dunnies are a vast improvement on the previous leaking, unhygienic bog.