One of the places which your parents would definitely love is Ljubljana. This wonderful city is repeatedly called the second Prague, because of its outstanding architecture. Nevertheless, it is much less busy thus all of these wonderful places and buildings might be seen with no lines (http://lot.com/airline-tickets/flights-to-ljubljana). Furthermore, even though you will most probably start such trip from the Ljubljana (as there are many cheap flights to Ljubljana), there are also a lot of other places which worth to see in Slovenia. E.g., in this small country you can see charming Alps and charming lake. And all of it is placed in less than two hours journey from Lubljana. Doesn’t this sound marvelous? Your parents will definitely love it!
Other spot which might be a good idea for a trip with beloved parents is Chicago. The generation of our parents very frequently perceives the United States as a rich and unavailable country. Actually, this makes sense if we think that most of people in their generation were going to Chicago not as visitors, but in case to find an employment.