It's a charming two-level apartment located in the very center of Vienna, just behind the Burgtheater. It was perfect for 3 of us, could easily suit 4 I think. The apartment is well equipped and has everything needed (some might miss a TV, we didn't). There's also an access to a patio which is a great bonus in a warm season.
The hosts - Sebastian and Sophia - are very friendly and helpful. We've really enjoyed our stay and hope to come back some day.