The "Phlegrean Fields"

Lake Avernum is an extinct crater now full of water, its sorrounding slopes densely wooded. The ancients imagined that the entrance to the underworld was near this lake, but it was in fact a Roman naval port, connected to the sea and Lucrino lake by a canal.
Interesting are the Grotto of Cocceio (at present closed to the public) and the so-called Temple of Apollo, probably the remains of a Roman bath which exploited the area's sulphur springs.