There are some fascinating places on this list, unfortunately I haven't seen most of them.  I have been along the Danube from Regensburg to Vienna, the scenery is absolutely gorgeous!
I would have liked to have visited Dresden, unfortunately during my stay in Germany it was in the DDR; my husband was in security in the Air Force, and it would have been difficult if not impossible to go there.  Same with Budapest, my best friend was there many years ago, from her pictures it looks fantastic, especially at night.
On the way to Antwerp, there was car trouble, so I never made it. Didn't get to Milan either.
Now I have itchy feet :) Hopefully I'll get to travel some more in this lifetime.