Via di Santa Costanza 53, home of the LUISS library, is the address the pin marks here.
Source: © Google Maps
The pin stands on Via di Santa Costanza 53, at its crossing with Via Nomentana and a little south-east of the roundabout with Via Bressanone, with the LUISS library labelled just to the north. The map also names Sant'Agnese/Annibaliano station, the Basilica of Sant'Agnese fuori le mura and the Mausoleum of Santa Costanza.