There was a fair amount of mold on the outer wall of the bedroom, from where the bed meets the wall to the ground, the entire length of the wall. My sister and I cleaned it ourselves the first night, because there was enough that it set off her allergies, and we didn't want to wait for that to get worse.
Beside that, the rest of the flat was clean, the amenities were new and worked well, the flat itself has windows on three sides allowing for a lot of light and fresh air, the bathroom was quite nice, the host's quick introduction to the city was helpful, and the location is great if you don't mind the uphill walk home. If it weren't for the mold I'd have given it five stars.