Australian passport-holders visiting Greece for tourism or business don't need a visa for stays of up to three months. For longer stays, a visa is required.
In the past, visitors with evidence of having been to Turkish North Cyprus have been denied entry to Greece. This seems to no longer be a problem, but to be sure, visitors may wish to replace a passport with a North Cyprus stamp or, if travelling to North Cyprus on the same journey, ask officials there, on entry, to stamp a separate piece of paper rather than a passport page, which they are sometimes willing to do.
For further information please contact your nearest Greece Embassy or Consulate prior to arrival.