There is so much variety in Europe, it's hard to give an answer without knowing a little more about them?
What languages do they speak other than English?
What sort of things do they like doing - outdoor / countryside stuff, museums, theature, restraunts, historical sites, cycling?
Are they active - i.e can walk about with ease - or do they need to get taxis from A to B? This will also influence the route - trains / ferries are more 'fun' but I wouldn't recomend this for someone who may have trouble walking up some stairs.
Is weather important? Even in the height of summer, the climate in the north of Europe - UK, Ireland, Germany, Scandinavia etc - is 'changable' to say the least

Give us a little more to chew on and I'm sure us Euroweanies can come up with some good ideas
