As described, the apartment is located in the basement of a typical Roman building. So don't expect much light or fresh air. The location is great anyway, just a 5-minute stroll away from St. Peters Square; the St. Peter railway station is also very close, and it is connected to the Roma Termini central railway station. The bus line 64 runs right in front of the building and can be taken to reach the city centre.
So the location is perfect for tourists.