A group of us decided at the spur of the moment to visit Vesuvius from Pompeii a few years back. I don't remember the details except that there was a ticket office for Vesuvius close to the Scavi station. We bought a round trip ticket for a bus that took us part way up the mountain. I am pretty sure that it was a privately run bus service, which is what our guide (who did not go with us) recommended. If I recall correctly, there is a public bus service that takes longer and runs less frequently -- but I may be wrong about that. Then, we transferred to a big all-terrain vehicle at the entrance to the Vesuvius national park. I don't recall whether our original ticket included the transfer or not. One way or the other, it was a simple transfer. It was a pretty rough, bouncy ride on the all-terrain vehicle. Eventually we arrived at the base of the summit and hiked another 30 minutes to the crater. Afterwards, we returned via the same route to the Scavi station, where we caught the Circumvesuviana back to Sorrento. I don't recall any of the process being challenging, which is probably why I don't remember the details.
My main recollection is that it was unbelievably cold and windy at the crater in October. Pompeii was a normal temperature, probably in the 60's or 70's. The crater was a good 20-30 degrees colder, with winds strong enough to make it challenging to stand up straight. Fortunately, there was a snack bar at the top, where I could get some hot chocolate and respite from the cold.
The excursion was well worth doing. There is something very eerie about the crater, with its huffing fumaroles --- much creepier than Etna. Also, there were beautiful views of the Bay of Naples from the summit.
