There is a bus service between Catania and the highest car park at the summit of Etna. Unfortunately, there is only 1 bus per day and this option is not suitable for most cruise passengers.
The AST bus from Catania to Etna Sud (the car park at the cable car to the main crater) leaves at 08.h15. The bus back from Etna Sud starts at 16h30. The trip takes 2 hours (one way) and the bus makes a short stop in Nicolosi.
Along the way you can enjoy some spectacular views along the flanks of the volcano. A ticket costs € 6.20 per person (return ticket). Better check the timetable in advance to see if it fits within your cruise schedule.
TIP: You can buy the ticket in the bar at the bus terminal.
How do I get to the bus terminal from the cruise port in Catania?
The AST bus leaves near the train station. Catania train station is located at Piazza Giovanni XXII, in the east of the city at about 1 km from the harbor. You can walk, take a taxi or use the subway. There 4 metros per hour and a ticket costs € 1 per person (valid for 90 minutes after validation).