OK so if you are into chocolate and cake then Vienna is the place for you! I have never eaten such nice cakes and chocolates (and I have been to Belgium - Sorry Belgian People)! Go checkout Café Demel I could easily put on a few kilos if this was in my town!
Architecture in Vienna can only be described as eccentric or old. You have old beautiful building or new buildings that just look crazy!
I would recommend going to the opera whilst in Vienna. Go to the State Opera House, it's a gorgeous Viennese theatre.
Whilst in Vienna you will stumble upon quaint little markets which sell both food and handmade good. I love shopping like this because I can buy unique items for friends and family.
One thing to watch in Vienna is the price - it's a little $$$.