Lake Avernus lies on the Tyrrhenian coast of Italy, about a mile from Cumae, filling the crater of an extinct volcano. Mephitic vapours rise from its waters, precluding life on its banks, because of which it was believed to be the entrance to the Underworld by the Ancients. Thus in Virgil's Aeneid, Aeneas sacrifices to the gods in the shadow of the forest surrounding Lake Avernus and then follows the Cumaean Sibyl into her cave and down in to the Underworld. However, the exact location is not certain but has been identified as including the 'Temple of Apollo' and the scene is based on views in the Phlegraean Fields, rearranged with Wilsonian licence. The elements are Lake Avernus, Lake Lucrino (middle distance), the Bay of Baia (distance). The mountain is Monte Gauro.
