From Leonardo da Vinci Airport
Train to Termini Station every 30 minutes, it takes about 30 minutes.
From Ciampino Airport
You first have to take a bus to Ciampino station (10 minute trip, buses leave every 30 minutes). Then 15 minutes in the train to arrive to the Termini station, 2-3 trains per hour.
From Termini Station
950 meters walk from the central gallery. Take via Marsala until piazzale Sisto V, leave the walls and take Via dei Ramni until Via dei Marrucini.