This apartment is fantastic in just about every aspect. The location is outstanding, as you are a 5 minute walk to the Vatican, St. Peter's Basilica, and St. Angelo Castle. The metro stop (Ottaviano is the closest) is a short 12 minutes away and other major attractions (Pantheon, Piazza Navonna) are 20 minutes away. The part of the street that the apartment is located on (Borgo Pio) is closed to vehicular traffic and is lively with many restaurants, gift shops, gelaterias, etc. The apartment is next to the Passetto (the Pope's "escape" route to St. Angelo); in addition, visible at the end of Borgo Pio is the entrance to Vatican City (gated entrance protected by Swiss Guards).
This was my 5th visit to Rome and I will DEFINITELY be staying at Federico's place again!