It's a basement made into an apartment. The apartment is just as in the photos - tiny, but cozy. It's very clean and well-kept. The bus stop is in front of the building and the place is very close to the city centre. Chiara is a lovely host, very responsive and communicative.
IMPORTANT! NOT RECOMMENDED IF YOU HAVE RESPIRATORY ISSUES!
It's an apartment located in the basement. There are only two windows in the apartment, one located in the main room, the other in the bathroom. The apartment is below ground level, while windows are on street level. The streets in Rome are quite dusty and dirty, so there's a lot of dust and dirt covering the windows and getting inside the apartment (it's also very loud, since you basically live under the street). The place is also surrounded by normal basements, so the air when entering the apartment feels a bit stale.
If you do not have any long term respiratory issues like asthma or allergies to dust, you'll be fine. (I have and so I had to change my place of stay after few days)