Vienna, Barcelona, and Rotterdam (plus someplace else) would be a lot of territory to cover in a nine day trip from the USA to Europe. You'd arrive into Vienna exhausted on the afternoon of day 2, spend perhaps days 3 and 4 in Vienna, fly to Barcelona on day 5, spend days 6 and 7 in Barcelona, fly to Rotterdam on day 8 and fly back to the USA in the morning of day 9? To me, that doesn't make sense, even without the fourth place.