I believe this is the first time I've left a completely five star rating, and definitely the best Airbnb I've ever stayed at.
The building was built in the Renaissance, and has lovely touches that remind you of that. However, despite being so old, it is quiet and well insulated. During a hot summer's day, one hour of air conditioning could keep the apartment cool the rest of the day.
The location can't be faulted, just a few minutes walk from Duomo, minutes from hundreds of restaurants, bars, museums etc.
The host of communicative and helpful. There is a check-in process that is required due to the age and location of the apartment. He was friendly and helpful throughout.
I cannot recommend this Airbnb highly enough.