The Cumaean Sibyl was a prophetess of Apollo with a special connection to the Roman state, which kept a collection of her prophecies, bought from her by King Tarquinius Priscus (see Servius, Aeneid 6.72), in the Capitolium. In Vergil's epic poem The Aeneid, Aeneas consults the Cumaean Sibyl, Deiphobe, for passage to the underworld. This photo depicts a cave traditionally identified as the seat of the Sibyl in Cumae and the entrance into Avernus.
A modern plaque cites lines 42-51 from Book 6 of the poem:
There's a huge cave hollowed out from the flank of Cumae's hill; A hundred wide approaches it has, a hundred mouths From which there issue a hundred voices, the Sibyl's answers. They had reached its threshold when "Time it is to ask your destiny" The Sibyl cried, "for lo! the god is with me." And speaking, There by the threshold, her features, her colour were all at once Different, her hair flew wildly about; her breast was heaving, Her fey heart swelled in ecstasy; larger than life she seemed, More than mortal her utterance: the god was close and breathing His inspiration through her. (translated by C. Day Lewis)