I like hospitals as much as beer (which means, not much). But the Stiegl Ambulanz at the Old Vienna Hospital (Altes AKH) is a different story.
Vienna's former grand hospital, dating from the 17th century, has now turned university campus and makes a wonderful hangout in the summer and winter. The Stiegl Ambulanz is a beer pub housed in the former walk-in clinic. It has loads of character, as does the whole historic compound.
The Salettl cafe in the compound is another beautiful place.
In the winter, the Altes AKH hosts a fab Christmas market. The 'Weihnachtsdorf' is a beautiful neighbourhood market where you have mulled wine, hot chestnuts, and can occasionally do ice skating and learn traditional crafts such as candle making and turnery.