One of those is Mill. It's located somewhat off the beaten path near Mariahilfestraße, which may be a reason why I've never heard of it before.
The outside looks innocuous enough, but one's surprised by a charming little courtyard that's extended into a roofed area that's equipped with massive tables and quite idiosyncratic interior design.
I haven't had any of the food, but the menu looks somewhere south of traditional Viennese, the waiters and waitresses are very friendly and once the courtyard needs to be cleared (round 9:45pm), the inside is just as charming.
Overall Mill's a nice surprise and it's definitely a place to dazzle non-Viennese with Vienna's gastronomical diversity.