One of the places which your parents would absolutely appreciate is Ljubljana. This incredible city is regularly called the second Prague, because of its outstanding architecture. Nonetheless, it is much less busy thus all of these marvelous spots and buildings can be seen with no lines (more information). Moreover, even though you will most presumably become such trip from the capital city (as there are lots of cheap flights to Ljubljana), there are also lots of other places which worth to see in Slovenia. For example, in this great country you can see charming Alps and marvellous lake. And all of it is placed in less than two hours journey from Lubljana. Doesn’t this sound amazing? Your parents would definitely love it!
Other place which may be a good idea for a trip with your parents is Chicago. The generation of your parents very often sees America as a rich and unavailable country. Actually, it makes sense if we think that most of people in parens’ generation were travelling to Chicago not as tourists, but in case to find an employment.