If you're thinking about Italy and Greece, I recommend the Appian Way from Rome to Brindisi (where you catch the ferry to Greece). It will take 10-14 days, depending on how often and for how long you stop. I just did this route a month ago, so if you email me I'll send you more info.

Anywhere you go in Europe, you're going to find fun and adventure. Keep your plans flexible. I like to have a starting point and an ending point, choose a few essential places to see along the way, and then be spontaneous about how I connect the dots.