I was visiting Vienna with a friend and we had a brill time, partly because Sabine and Christopher's apartment served as our headquarters! They were very helpful and answered all our questions within a day. Unfortunately, we didn't meet in person because our holidays collided, but they had the lovely Eve to let me in and give me the tour. They were also very accommodating since I arrived in the morning, hours before my friend, and still let me take my luggage there and relax after my trip.
The apartment was close enough to the city centre that you could walk there (it would take half an hour or so though) but the underground connections were favoured by us. They will take you anywhere and so fast! The apartment was also very clean and in a quiet neighbourhood. What we particularly liked, and why we eventually chose to spend our week at S&C's place, was the kitchen. We preferred to make our own breakfast so having flour, oil, etc. plus cooking equipment ready was fantastic. There were stores close by too, a Billa and a Spar both, so you could get everything you need in a matter of minutes. All in all, we had a great week in Vienna. I'd definitely recommend S&C's apartment. Anyone would have a lovely time there!