I stayed in the single room.
Pros / To keep
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1) Amazing location // Right in the very heart of the city. Walking distance to absolutely everything! Furthermore, you cannot feel more safe than in one of the most central streets of Bologna.
2) Communication // Friendly hosts. Availability for late check-in, even with the added cost.
3) Really good heating and available A/C in the room.
4) Nice decoration.
5) Security door in the apartment.
6) Clean and spacious bathroom (+ a personal hairdryer).
7) Big closet.
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Cons / To improve
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1) When I arrived, late at night (00:45), and after Ivan showed me around and left for the night, I noticed that the bed sheets and pillowcase seemed as if they were kind of used. Not that they smelled particularly, but they were wrinkly and kind of worn out from use. I messaged Ivan and sent him a photo; he responded immediately (+++ for the availability) he reassured me that there was not case whatsoever the lady that cleaned the rooms did not change the linen, but said it was possible that they just were not stirred by the laundry service. He guaranteed for her and since it was late at night and no solution seemed to be available, I had to take his word on it. The other day he messaged me that he contacted the lady that cleaned and she categorically supported his case as well, and offered to tell her change the linen then if I wanted to. Since I had already slept there, I didn't find any reason to ask for this. Anyway, this did not make a good impression.
2) Paper thin walls. I was hearing even the calm discussions by the girls next door. Hopefully they were not very noisy.
3) There was some noise from the street too
4) Darker drapes needed to keep the light out. If you're used to sleeping in the dark, you'll wake up early in the morning.
5) Towels are too thin.
6) No mini fridge available in the room.
7) For long stays one may find it difficult to fit a bigger luggage in this small single room.
All in all the apartment is a good choice, and offers a very good value for money for Bologna prices. Its location could do the trick by itself. If the linen/pillowcase issue was somehow solved (or not present to start with) I would be even more inclined to recommend it. Reading all the other very positive reviews (that made me choose this room) I hope this issue was just an exception.