A very nice flat with excellent hosts. I would definetely come again.
My experience with the stairs: For healthy people of any age they are doable, nothing to fear of. My 70yo mother had no issue with them. In case you have any mobility issues though. I wouldn´t recommend this flat.
A small con: The front big bedroom has windows to a main street, which is loud at almost all times of the day and night. After 02:00 in the morning, young party people go through the street literarily screeming (obviously drunk after getting out of the nearby bars). Every 10ˋ it is another company of people walking through screaming, so you cannot just call the police each time. In the morning from ca 08;00 the street gets busy again. In other words: It is almost impossible to sleep in that bedroom without earplugs (closed windows, of course). The other 2 bedrooms do NOT have this issue, since they are in another side street. Apart from this, I cannot find any other con for this flat, it was all fine!