Our stay in Vienna was great, also, thanks to Katharina's apartment :) The flat is cosy but has enough space for two people with all needed facilities (kitchen equipment, towels, etc.). It is clean and warm (considering weather in Vienna it is important :D)!
Can't help but mention that all the details like candles, pictures and small notes make the place living and, thus, our stay was mellow :)
The apartment is located close by public transport to all important sightseeing and museums which is definitely an advantage because it is easy to reach city centre or other parts of the city, for example, Belvedere or Prater de Vienne. Plus, around you will find many grocery shops and restaurants.
And last but not least, the communication with Katharina was great: prompt and pleasant.
I really recommend staying at her place.