Funivia dell'Etna runs a cable car from Rifugio Sapienza (1923m) up the mountain to 2500m. Once out of the cable car you can attempt the long walk (3½ to four hours return) up the winding track to the authorised crater area (2920m). If you plan on doing this, make sure you leave yourself enough time to get up and down before the last cable car.
The ticket office accepts credit cards and cash.