For a fun thread... This summer I will be in Austria and will be in Vienna for a total of 5 hours on a Sunday. I have been there many times, but the last was 7 years ago. If you had only 5 hours, what would you choose to do? I'm torn betwenn chilling out near the Graben, sitting in a cafe, and going to Karlskirche (it has always been under construction every time I've been there). Maybe hitting up the park with the "Golden Strauss" and St. Michael's church. Or... I could hoof it over to Belvedere or Schonbrunn and spend sometime in the gardens there. Oh the choices! :)
It seems to me that you know the answers to your question. How would a group of strangers know more about what you want to do than you?
You certainly cannot go wrong with Schonbrunn or Stadtpark (with the golden Strauss). Consider taking the U out to Ottakringer Brewery and Store, where you can taste and shop in a non-touristy Vienna district.
I'm just back from Vienna and I'm an art lover, so I'd go to the Bevedere. Five hours would give you time to see it and get a nice piece of cake somewhere in the city center (Oberlaa in Neuer Market?). If you are a music fan, I highly recommend the Haus der Musik. You could also do the Imperial Treasury if you want a bit of Hapsburg history. Karlskirche is still under renovations, but you can take an elevator and stairs up to the top of the lantern which is pretty interesting. We also really enjoyed the Wien Museum next door.
Great suggestions. Thanks you guys!
If you are there early enough and are a music fan, the 11:00 mass at the Augustinerkirche is a full music mass with choir and orchestra. It is right next to the Hofburg Palace, so it's close to other things you may want to do.