Figure above:

Painting by Jacob Philipp Hackert, realized in 1794, and now in the Neue Pinakothek, Munich, Germany, representing the Lake Avernus, near the promontory between Cuma and Pozzuoli.
The lake is placed into the crater of an extinct volcano, and on its shores, once profusely covered with vegetation, there were sacred groves dedicated to the goddess Hecate. The exhalations rising from its waters were considered by the Ancients lethal for the birds which flied near the lake, and it seems that the place name meant properly the lack of birds, from the Greek Aornos “birdless”. The physical characteristics of the landscape determined its fame as an entrance to the Underworld. In its neighborhood opened the cave of the Sybil of Cuma, through which Aeneas went down in the world of the dead (Aeneid, VI, 106-107).
The prophetess was regarded as minister of Hecate-Diana, who assumed the epithet of Trivia (Aeneid, VI, 35), because she was worshipped at the crossroads (still in the Middle Ages are reported visions of parades of the dead which could be met at crossroads, privileged places of interaction between the world of the living and the world of the dead).


[Image: http://commons.wikimedia.org/wiki/File:Jacob_Philipp_Hackert_-_Lago_d%27Averno_-_WGA11023.jpg]


Figure below:

View of the solfatare (fumaroles) at Pozzuoli. The area of the Phlegraean Fields, like the nearby Lake Avernus, was regarded as a placed from which it was possible to reach the Underworld. Ancient tradition has set in this landscape the fight of the gods against the Giants, which the Greeks had originally placed in the plains of Phlegra, in Thessaly.

[Image: http://www.fotoeweb.it/sorrentina/CampiFlegrei.htm]