The S20 is a railway service that runs every half-hour between Castione-Arbedo and Locarno in the Swiss canton of Ticino.

Treni Regionali Ticino Lombardia (TILO), a joint venture of Swiss Federal Railways and Trenord, operates the service.

The S20 runs every 30 minutes between Castione-Arbedo and Locarno, using the Gotthard line from Castione-Arbedo to Giubiasco and then the Giubiasco–Locarno line to Locarno.

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