If you are planning to visit Vienna, there are a lot of things to see and do. If you just have a day or a few days in Vienna the good thing for you is that you will find the most popular tourist attractions along the Ringstrasse in Vienna.
If you are interested in history and old buildings, the Ringstrasse is the place to go to. Along the Ringstrasse you can find the impressive Vienna State Opera (picture). From here it is only a short walk through the pedestrian zone of the Kärntner Strasse to the famous St. Stephan's Cathedral.
Furthermore there is the Parliament Building, the beautiful old building of the Kunsthistorisches Museum Vienna, the Town Hall, the National Theater and many more buildings along the street.
If you are just here for a quick visit and want to see as much tourist attractions as you can, I recommend a Hop On Hop Off Tour through the City, so you can see all the sights and you don`t need to worry about the transportation in the city. You can also combine this tour with another tour to see even more tourist attractions if you have time for that. Just see the link below for more information. I personally would recommend to spend at least 2 or 3 Days in Austria`s capital and largest city.
More information about the city tour: viennasightseeing.at
More information about the Ringstrasse: Wikipedia