Final answer:
Aeneas visits a secluded valley by the river Lethe in the underworld to speak with his father, Anchises, who reveals to him the future and the fate of his descendants, which is a key narrative of Virgil's epic poem, the Aeneid.
Step-by-step explanation:
Aeneas had to go to the underworld to receive knowledge of the future from his father, Anchises. This encounter takes place in a secluded valley by the river Lethe, a place where souls destined for reincarnation drink from the waters of forgetfulness. During this visit, Anchises explains to Aeneas a detailed Stoic cosmology and anthropology and discusses the nature of the soul, giving Aeneas insight into his future tasks and the future of the Roman people. This is a part of the narrative in Virgil's epic poem, the Aeneid, which is an important text in classical studies and often studied in the context of high school English or literature classes.