Casa Marietta, is a surprise. It is a lovely tiny house at the end of a small alley surrounded by much larger buildings with several apartments in it. Though small, the house has everything, small kitchen, living/dining space, bathroom and bedroom (quite large) at the first floor ( under the roof). What makes it really special is the roof terrace next to the bedroom. On the picture at the Airbnb site it seems relatively small, but in fact there is quite some space. It is wonderful to sit outside on the quiet roof terrace, looking at the sky and the buildings and listening to and looking at moments of city life in front and around you. It should be mentioned, that the stairs to the first floor are doable with care, but quite steep.
On top of that, Casa Marietta is indeed in the middle of the old city, in a side street of the Via Vittorio Emanuele II, one of the main city arteries shaping the centre. It is an excellent starting point for sightseeing, walking around the old city centre (it is less than 15 minutes to the Piazza del Duomo).
Communication with Anna Maria, Daniele and his sister was very pleasant and they were amazingly helpful in particular when we thought we had lost the key of the apartment (and happily found it back again). Altogether an excellent place to stay for visiting and experiencing Catania.