Mount Vesuvius is the most famous, indeed iconic, volcanic feature. But the entire Bay of Naples area is a large volcanic complex. The largest caldera is actually on the opposite side of Naples to Vesuvius: the Phlegrean Fields.
These pictures were taken in the Solfatara crater, between Naples and Pozzuoli. They show the volcanic steam (mixed in with other more noxious gasses) coming from the fumeroles. The bright yellow on some rocks is flowers of sulfur, condensed out from the gasses emitted.
What the pictures don’t show is that some parts of the crater are perceptibly hot to the feet through shoes.
These pictures couldn’t be taken now. Since 2017 the crater has been closed to access because of safety concern prompted by rising seismic activity.