This is a really lovely, light, airy, very clean and elegant apartment. We were two people staying 4 nights, and really enjoyed our time in Vienna. The location of the apartment is very good, as described is very close to the metro, and we walked to and from the centre of the city on one occasion so very accessible. It's in a lovely old building, and as other users have said definitely worth the walk up the stairs. Comfy bed, good quality sheets etc, plenty of hot water, good shower and whatever we needed was in the kitchen.
The information provided by Max was very useful, we walked to and ate at Restaurant Steman on our first night, it was very typically viennese and excellent.
The apartment is absolutely recommended.