Saint Stephan Cathedral in Vienna is one of the city's symbols and the sitting place of the Catholic Archbishop of Vienna.
The cathedral was built in 1147 and rebuilt in a gothic style in the 14th-century.
When I visited, it wasn't possible to see the whole church because of a fence they built to avoid access. However, they were arrangements for a concert, so maybe it is possible at different times.
In any case, this is an imposing church located in Stephanplatz, the most central place in the city, so it is worth paying a short visit.