Didn't go to Vesuvius, but went to Pompei, saw lots, was there about 3 hours, but i would say it would take 2/3 days to see it all. Guide was brilliant. We went in Sept it was scorching so take a hat and plenty of water, we bought one outside and they were v expensiv.
Was that on the full day Island or another tour, was lookng at goole dont fancy the coach trip up the side of vesuviu.
Pompei is a must do. The train station is right outside the entrance to the ruins - train runs from Sorrento if that's where you are stopping ( if it's Naples - good luck crossing the road that separates the port from the town - don't exp[ect them to pay any attention to the pedestrian crossings!!!!!!!!!) Agree with Foster , Pompei needs subsequent visits to fully appreciate it.
Mount Etna trip takes you to a bar/cafe by the side of the road, from where you can take a walk round a crater. This is fairly smooth going, but it gets very cold up there. The day we went it was sunbathing at sea level and snowing at Etna.The trip is well worth it for the scenery on the way.