The building, as well as the appartment is a fantastic place.
I liked the nice mix of vintage/contemporary.
The appartment is very well equiped (for cooking, breakfast etc.), including beverages in the fridge from 1€ (appreciated).
Take the time to read the docs provided by Markus, they are helpful.
The location is nice as well: you can walk to any place within the ring and we liked to wander in the nice Streets around the appartment before going to the shopping/muséums area.
Markus himself was very welcoming, helpful and flexible.