The city of Napoli (Naples) is located between the volcano Monte Vesuvio and the sea, at a wide cove named Gulf of Naples, which ends to the north at the island Ischia, and to the south at the island Capri. The climate is warm, the soils are fertile, the city with its almost one million inhabitants is located on a small strip of coastal plain and the lower flanks of the Vesuvio. The area is dominated by volcanism, there is Mount Vesuvius in the center of the gulf and the Campi Flegrei (Phlegraean Fields) at the northern side of the gulf. Vesuvius is actually an extremely dangerous volcano, it erupted with a violent explosion in 79 AD and created a typical cloud. This eruption was described by Pliny the Younger, a famous Roman writer, and this kind of eruption was later named Plinian eruption by the geologists. The volcano, like nearby Phlegraean Fields, shows some activity, like emanations of carbon dioxide and sulfur, hot spings, mudpools, and more. But there hasn't been an outbreak for a long time, which is actually not a good sign, because the longer the outbreak lasts, the worse it gets. There will be a major eruption, and like the one which destroyed Pompei and Herculaneum in 79 AD it may destroy most of the city and kill a million inhabitants.

The volcanism of this area is explosive, there are no lava streams flowing down the mountain side, and hence there are no lava tubes. The sites we listed are primarily based on Roman subterranean architecture and Roman and Medieval catacombs. The southern edge of the gulf including the island RegionCapri are composed of limestone, and there are numerous karst caves.