From Ciampino Airport:

Shuttle bus to Anagnina Subway Station.
Subway Line A (red) get off at Flaminio-Piazza del Popolo stop.
Tram #2 get off at Apollodoro stop.

From Fiumicino Airport:
Light train to Termini Station.

From Termini Station:
Subway Line A (red) get off at Flaminio-Piazza del Popolo stop.
Tram #2 get off at Apollodoro stop.

By car:
Ask for the Auditorium-Parco della Musica.