The apartment is located very conviently between the central train station (Hauptbahnhof) and Rennweg. The building is in an inner courtyard so there is no noise from the street.
The apartment is on the sixth floor, directly under the roof (but with normal ceilings and windows). There is a elevator till the fifth floor. The apartment is small (bed=couch), but everything you need is there.
The host was nice, responded quickly and was flexible.