I think it is worthwhile to point out that it is possible to say "It is worthwhile to visit Greece," even if we would more commonly say "Greece is worth visiting."
The sentence "It is worthwhile to visit Greece" means "To visit Greece is worthwhile."
Interestingly, H. W. Fowler objected to sentences like "It's worth visiting Greece" (assuming "it" is a placeholder), since we can't say "[strike]Visiting Greece is worth.[/strike]"
That said, I think Fowler would have been fine with "It's worth visiting Greece" if "it" referred to something and the speaker considered it undesirable to visit Greece.