In my dad's collection of 'WW2 Italy' photos are 3 which have the words "The Lake of Hell" hand-written on the back. I don't think there can be any doubt that these are photos of Lago d’Averno (Lake Avernus) which is a couple of miles west of Pozzuoli (Naples). My dad spent the first half of 1945 close by there. Lago d’Averno is a volcanic crater lake, which the Romans thought was an entrance to Hades, the underworld. It may look harmless to our eyes, but this area could 'blow' at some point in the future. The last time Vesuvius erupted was in March 1944, when the lava flowed towards my dad's HAA Battery site, which was a short distance away. They moved further away about 10 days later to Pozzuoli, but may well have been in just as much danger. The whole area is part of an active volcanic system, which is now considered one of the most dangerous volcanic areas in the world.
Thank you for posting Steve very interesting 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 lake is roughly circular, measuring 2 km (1.2 mi) in circumference and 60 m (213 ft) deep. Lake Avernus - Wikipedia