North Italy/Slovenia: the western Carso, around Gorizia and the grotesque Italian Facist-styled war cemetary on Repuglia/Mt Sei Busi. As a caver I'd also like to have a look underground at where the Austrians modified natural caverns during the fighting there in WWI. I read a superb history book about the awful war fought there in 1915-18 and would like to see the place. My OH has done via ferratas in the Dolomites but I wasn't interested at the time so didn't go - wish I had now (she is no longer up to climbing worse luck).
I'd also like to visit the remnants of the giant frontier fortresses in Flanders, espcially those built by Vauban ~1700. We had a walk around one and it was so big we had to give up after 2 hours.