Accompanying Eric Kandel to New York's wonderful Neue Gallery. Perhaps the best collection of Austrian and German fin de siecle art outside the Belvedere in Vienna.
Reasons to visit Vienna: Coffee, pastries, horses, the Belvedere and the Kunsthistoriches.
You can't "do" the latter any more than you can do the Prado. It's like the Metropolitan in NYC, but Vienna has the best collection of northern European art (thanks to the Hapsburgs). We went there to see the Breughels, and that was enough. Mind-boggling.
Well, we went to the Opera too.