"Vulcan's cave" at the entrance to the Solfatara, near Naples: jets of steam emerging from the rock floor, watched by spectators. Etching.

"The crater of a half-extinct volcano known to the ancients as Forum Vulcani. ... The path along the bottom passes (l.) a well of hot water 9m deep and soon reaches the Fumarole, a number of violent jets of steam emerging from the ground at a high temperature (c. 143 degrees C) and charged with sulphurous vapour. The nature of the gas varies considerably. The ground is hot and makes a hollow sound when stamped on. ..." (P. Blanchard, Blue guide Southern Italy, London 1984, pp. 189-190)