Simone's apartment is located just a few minutes from Roma Termini by taxi (and, according to Google Maps, 20 minutes on foot).
It was easy to reach, easy to self-check-in, and, more importantly, very easy to get to.
There are plenty of cafes, bars, gelateria, and restaurants in the vicinity. While the Trevi Fountain and the Spanish Steps are just a few minutes away on foot - avoid the crowd, go there early in the morning or late at night. The Vatican is about 16 minutes by taxi.
The apartment was quiet, very comfortable, and clean. Honestly, I was pleasantly surprised by how spacious it was.
Simone was quick to respond to any queries and was generous with recommendations to help make our visit memorable. We are definitely going to try and stay there if we go to Rome again.