That's not Vienna's cathedral, which is St Stephen's, and which has a single large tower. The above one is the '
Votive church' and is actually 'modern', built and completed in the late 19th century - which goes to show you that such stunning 'gothic' architecture was still within human competence not all that long ago!
Here's Vienna's cathedral, which is jaw-dropping, both inside and out, and which still dominates the city's skyline. It was (mostly) built in the 14th century: