I stayed in Lena's apartment for a week and it was a great experience. The place is spacious, quiet and it was really clean. It had all the amenities that you will need for your stay and the internet was good. The best thing was the location, as you are just a few minutes from many cafes, restaurants and shops and the main thing - 10 minutes walk (even less) from the Museum Quarter. Lena was very responsive and really helpful and she met me in person when checking in to show me the apartment.
If I am back in Vienna, I will definitely stay here again! Thank you Lena & Alex!