From Turin airport:
A train connects Caselle Airport to the Dora GTT station in the city of Turin. From Dora GTT train station take number 11 bus at the stop in Via Stradella and get off in Via San Tommaso. Turn left in Via Santa Teresa and walk as far as Piazza San Carlo (approximately five minutes on foot).
Alternatively, there is a bus service connecting Caselle Airport to Porta Nuova train station.

From Porta Nuova train station:
From Piazza Carlo Felice exit walk to Via Roma, then to Piazza CLN and keep going until you reach Piazza San Carlo (approximately ten minutes on foot).