Are you in Rome or London and just feel like visiting Athens? What a stupid question, of course you do!
So then i would recommend you to check out olympicair because they have the best offers right now! From Rome to Athens its from only 26 euro. And if you would like to get away from the rain in London to get to the sunshine in Athens, that would only cost from 32 euro. And this is including the taxes and service charges!
Easyjet also have alot of nice offers right now, so check them out aswell.