Graz is the state capital of Styria; the historic city center has been declared a UNESCO World Cultural Heritage Site. In the center of Graz is the Schlossberg (castle mountain) with the symbol of Graz, the Uhrturm (clock tower).
At the foot of the Schlossberg are among other things the Herrengasse, a Baroque boulevard, the Landhaus with an arcade court from the Renaissance, the city hall, and the city's parish church.
Duration of the trip approx. 10 hours; the journey between Vienna and Graz lasts approx. 2 1/2 hours.
Of course you can take trips from Vienna in the provinces.
These last depending on the distance half or full day. For more intensive sightseeing I recommend two days.