As Vienna is a possible let me give a mix. Spend a few days there and then venture over to Bratislava which is one hour away and spend a few days there.

Antwerp/Bruges/Ghent would also make for a nice week.

I like Barcelona but damn last time we were there in late September it was over run by tourists. Painfully over run. We found Sevilla to be much reasonable. And would combine with Cordoba/Granada. Madrid is also reasonable.