Our stay at Constantin's newly-remodeled top-floor apartment (Sky Gallery) was fantastic. The place is brand new, with a nice outdoor terrace, nearby groceries, restaurants, and parks, and of course very close proximity to the center of Vienna. We walked nearly everywhere we wanted to go, but also biked using the nearby CityBike rental station a block away. An Ubahn subway station is also a block away, which we used to get to the convention center. Constantin was a great host and we very much enjoyed meeting him. The photography (many originals by Constantin) really added to the atmosphere of the place. Another family stayed in a different Airbnb apartment a short walk away. Their place was also nice, but not as cool as ours. I can't think of anything negative to say. I even met a couple of neighbors and they're super friendly. You can't go wrong here. My family will always remember that apartment and the time we spent in Vienna.