Aeneid: Unexpected Journey Part III

Sailing away from Africa and Dido's drama, they were at sea for days before they reach Sicily again. This time they were guests of Acestes, in Eryx. Acestes' mother was Trojan, so he helped Aeneas prepared a great funeral games for Aeneas' father, Anchises, who had died at Drepănum a year ago.
Then they set out again for Italy, hoping to reach Cumae, so he could consult with the Sibyl. Before they had landed in Eryx, Palinurus, the pilot of Aeneas' ship had complained about dark, stormy sky. But before they reached Cumae, the pilot was lulled by the calm weather and sea; he fell asleep at the tiller, then fell overboard and drowned by Somnus, the God of the Sleep.

The Trojans reached Cumae, where Aeneas found and met the Sibyl, the oracle and priestess of Apollo and Diana in Diana's Wood. Her name was Deiphobe, daughter of Glaucus. Through a trance Sibyl foresaw that Aeneas would find greater danger in Latium than he ever did on the high seas. In Latium, Aeneas would have to fight another war, if he was to win a homeland for his son and people.
Aeneas was not satisfied with just Sibyl's prophecy, he wanted to go to the Underworld to visit his father; a promise he had made before Anchises had died. The Sibyl agreed to guide him through the Underworld, only if he could find the Golden Bough.
The Golden Bough was sacred to Proserpine (Persephone), which will be offered to the goddess. Another name for the bough was the Wand of Destiny. Like the name implied, the leaf and stem is golden in colour. Pluck the bough from the tree, and another one would grow in its place. However, no one can pluck this Golden Bough, unless the person was destined to do so; not even an axe or sword could cut the Bough from the tree. It can only found on one tree, somewhere in Diana's Wood. Aeneas felt a little despair, because this wood was quite large and dense. A white bird flew pass Aeneas' face. The Trojan hero recognized the dove, which was sacred to his mother. He believed that his mother had sent the bird to aid him, so he followed the flight of Venus' dove.

Aeneas found the Golden Bough on a holm-oak tree. Aeneas had to pull a couple of times, before the Golden Bough would come free in his hands. Aeneas brought the bough to the Sibyl, and they made preparation to descend the Underworld.
Aeneas and the Sibyl went to a cave, which was protected by a black lake and forest. No birds fly over this lake because the fume or water vapor was poisonous. Four bullocks were sacrificed to the goddess Hecate. Aeneas, himself, sacrificed a black lamb the Fates and barren cow to Proserpine. After sacrificial rites were completed, Aeneas followed Sibyl into the Underworld.
There is a lot of description in Aeneas' descent, which cannot be fully described here. Aeneas and Sibyl on had to the river Styx, where they encountered Charon, the ferryman. At first, Charon refused to allow passage for the livings, because of his previous dealing with living heroes (Heracles, Orpheus, Theseus and Peirithous). He change his tune when the Sibyl revealed the Golden Bough to Charon.

The Sibyl had also led them passed the Cerberus, by feeding them drugged honey cakes, which caused the hound to fall into slumber. Throughout their journey, Aeneas encountered shades of human and some shades of frightening creatures, but now harmless now that they are dead. Among the shades he met was his cousin Deïphobus, son of Priam. But the person who caused him the most grief was Dido, the Carthaginian queen. Dido refused to acknowledge his presence, since she had killed herself because he had abandoned her. Even dead, she was still angry with Aeneas. She has now rejoined her former husband, Sychaeus, who comfort her.
They soon came to the entry to the Elysian Fields, where an archway was erected by the Cyclops. At this gateway, Aeneas planted the Golden Bough on the threshold, before the pair entered a separate part of the Underworld.

Sibyl then asked the poet Musaeus for direction to finding Anchises. Musaeus was either a pupil, lover  or son of Orpheus. Finally they found Anchises near the river Lethe. Father and son were reunited for a little while. Anchises urged his son to find their new home in Italy, where one of their descendants, named Romulus, would find the city Rome that would last thousands of years. Anchises also revealed that this Rome would establish a strong empire, lasting longer than others; it would certainly be greater than Troy.He mentioned other kings and famous generals, as well as the wars against Carthage and Gaul. Few of these great Romans would be:

Gaius Julius Caesar: Great General and Founder of the Roman Empire

Augustus (Octavius), the first emperor of Imperial Rome

Trajan: Emperor and Conqueror 

Hadrian: Emperor and great architect 

As you can see this is a lot of propaganda for Rome or their destiny.