i did a month in Europe solo when i was 20, in the year 2000. this was pre smart phone. with a smart phone it (Europe) has zero challenge.
i think for europe, cruise are more of a supplemental "treat" and free roming on your own is the way to go. renting a small car, setting you gps map on your phone to avoid freeways and setting out. such fun (i couldn't rent a car in 2000)