My partner and I are bringing my 22 year old daughter and her friend to Athens. On day 3 we are parting ways...they are going island hopping and we are touring the mainland. My question is, is it safe to send them via metro to Piraeus and let them find their ferries on their own, or should we take them there? They are smart, streetwise girls but don't speak a bit of Greek. Perhaps I'm being over protective. Any advice???