The hosts were amazing, gave us lots of great tips and an annotated map of places to visit. The flat itself is right in the center of the old city, surrounded by things to do.
The only reason for 4 stars instead of 5 is that the appartment is quite noisy because of where it is, you can hear the neighbours quite a lot and because you're right above the restaurants you get some strong wiffs of food cooking late into the night.
That is inevitable with how central the location is, and in my opinion definitely worth the tradeoff.