The apartment is located in the city center (on foot: 15 min from Secession and 20 from the Staatsoper, 30 min to the Museum Island) inside an historical 19th century building. It's located at the third floor but the stairs are wide and not at all steep. There are a couple shared places (veranda, inside court from the ground floor entrance hall, kitchen) and the entrance hall is particularly comfortable to manage your luggage when checking out as we did on the last day. Checking in was also very straightforward.
Valerie is a great host and upon giving us instructions on the chat also managed to meet us as not to get confused with our keys.
The apartment is bigger than what it looks like in the photos. We haven't used one of the bedrooms as we only needed one room for all our luggages and stuff. The bathroom is also very large and can host more than one people at once. A lot of light shines through the large windows but they close well and also the curtains do a good job obscuring them. The only con, which is explained by the age of the apartment complex, is that the wooden floor cracks quite a lot. Really a great place to stay in the middle of Wien.