A really comfortable, clean and spacious apartment in a fantastic location. Just a short walk to the underground and CAT to airport, 15 minutes to Karlskirche, even close to tram stops: 3 minutes takes you to the park and a late-opening grocery shop (handy if you arrive late and want to grab something for breakfast next morning). The beds were extremely comfortable and the whole apartment was spotless. The apartment was so quiet it was hard to believe you were in a capital city: there was some general building work taking place, but given that we were out and about all day, it didn't have any impact on us at all.
We would have no hesitation in recommending Daniel's place to anyone visiting Vienna.