Best ticket for public transport (3 days): 72h Vienna + airport <-> Vienna (not cat)
Recommended places: Prater, Hundertwasser building, Ringstrasse, state opera house, Imperial palace (!), St. Stephen's Cathedral
Lots of museums if you are interested ;)
lovely historic city. try to visit this place in the middle of january every year. many fiesta or festival are held during that time and make the city become more live. the old buildings are well preserved