Karl's apartment is lovely and even bigger than in the photos.
Super clean and nice and warm (We were in the minus 1-4 degrees and snowing and we did not feel a thing inside the flat).
It is only a short walk away to Spittelau underground and you have multiple connections from there to the rest of Vienna.
Comms with Kati were great. All th way from the booking to the check-out.
She also gave us some really nice dinning suggestions.
I would recommend Kati's apartment to everyone travelling to Vienna.