I was a little disappointed by vienna, to be honest. I'd dreamt about going there for years, even about moving there, but I found it much too dirty and smoggy and unfriendly. I'd strongly recommend going to Salzburg instead. However, if you are to list reasons for Vienna, it's got to be the operas and music - Vienna is full of concert halls and orchestras. Ten there's the amazing architecture, or the millions of art galleries and museums, or the city's rich and interesting history. The city is steeped in culture, and has a wide variety of traditional foods. There is, of course, the language, and many other interesting things such as the Spanish riding school, or the castles.
To name but a few.
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"God kissed her on the cheek and there she was."