Lago d'Averno

Lake Avernus (Italian: Lago d'Averno) is a volcanic crater lake located in the Avernus crater in the Campania region of southern Italy, around 4 km (2.5 mi) west of Pozzuoli. It is near the volcanic field known as the Phlegraean Fields (Campi Flegrei) and comprises part of the wider Campanian volcanic arc.

The Grotta di Cocceio (Cocceius' Tunnel) is an ancient Roman tunnel nearly a kilometre in length connecting Lake Avernus with Cumae and dating from 38-36 BC. It was burrowed through the tuff stone of Monte Grillo by the architect Lucius Cocceius Auctus at the command of Agrippa who was in the process of converting the Lake into a military port, the Portus Julius.