Perennials gardens in southern Europe ?

I'm an Italian student and I'm studing to become a good gardens and landscapes.
In particular, I'm trying to specialize in the family of herbaceous
perennials.
I plan to make a long trip to Europe to study gardens projects which make extensive use of herbaceous perennials.
Could you please advise me what are the most interesting gardens in Europe,
to study this family of plants and their combinations?
You know, please, a list? a website or a book (in English)?
In particular, could you please tell me if there are gardens of perennial herbaceous in southern Europe where the climate is closer to the Italian one?
Hopefully you'll find the time to answer because I wrote to other
associations and nobody has ever responded.(If you prefer, you can answer me in French).
Thank you very much for this valuable information.
Sincerely
Marco
Jesi-Ancona-Italy