Unfortunately, the apartment did not match our expectations at all. We were warned about the size which actually was not problematic since we stayed there as two people.
The main issues were the state the whole apartment was in at the time of our stay. It was shabby and worn down. Crumbles and traces of liquid were coming from the ceiling, the shower did not function rightfully and the toilet was way to small for a normal person to use with the door closed. I have to be honest and say that we did not enjoy our stay there.
On the contrary, the communication with the host was terrific. After explaining the situation they were understanding and reasonable and agreed to a part-refund as a reimbursement for the troubles. I would not complain that much if the apartment was cheaper (~73€ per night incl. AirBnb-charges). The hosts promised to get the apartment to an appropriate standard in the near future.
Thank you again for being so insightful.