I cannot believe Andreas does not charge a lot more money: the flat, the hospitality, and the location were amazing.
The flat, which sits on the top floor of a building (don't worry: there's an elevator), was beautiful with lots of art and exposed wooden beams. The bedroom was similarly beautiful and had high ceilings and electrically controlled skylights. The bathroom was very modern and clean.
Andreas and his wife were very welcoming. When I asked for advice regarding exploring Vienna, they were able to make some good recommendations. They also twice invited me to join them for breakfast, which was very good and included some interesting things I had never tried before. There were also a number of friendly, thoughtful touches, such as leaving a bottle of water and a chocolate on my bedside table, which was made from a beautiful piece of wood.
I cannot think of a better location: it is a two-minute walk to Hofburg Palace, a one-minute walk to St Peter's Church, a three-minute walk to St Steven's Cathedral, and no more than a five-minute walk to many of the famous cafes.
I would happily return in an instant!