The city of Napoli (Naples) is located between 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 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 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 has been no eruption for a long time. There will be a major eruption, and like the one which destroyed Pompei and Herculaneum in 79 AD it may destroy 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 primarly based on Roman subterranean architecture and Roman and Medieval catacombs. The southern edge of of the gulf and the island RegionCapri are composed of limestone, and there are numerous karst caves.