The journey to Hades begins

His actis propere exsequitur praecepta Sibyllae.
spelunca alta fuit vastoque immanis hiatu,
scrupea, tuta lacu nigro nemorumque tenebris,
quam super haud ullae poterant impune volantes
tendere iter pennis: talis sese halitus atris
faucibus effundens supera ad convexa ferebat.
quattuor hic primum nigrantis terga iuvencos
constituit frontique invergit vina sacerdos,
et summas carpens media inter cornua saetas
ignibus imponit sacris, libamina prima,
voce vocans Hecaten caeloque Ereboque potentem.
supponunt alii cultros tepidumque cruorem
succipiunt pateris. ipse atri velleris agnam
Aeneas matri Eumenidum magnaeque sorori
ense ferit, sterilemque tibi, Proserpina, vaccam;
tum Stygio regi nocturnas incohat aras
et solida imponit taurorum viscera flammis,
pingue super oleum fundens ardentibus extis.
ecce autem primi sub limina solis et ortus
sub pedibus mugire solum et iuga coepta moveri
silvarum, visaeque canes ululare per umbram
adventante dea. ‘procul, o procul este, profani,’
conclamat vates, ‘totoque absistite luco;
tuque invade viam vaginaque eripe ferrum:
nunc animis opus, Aenea, nunc pectore firmo.’
tantum effata furens antro se immisit aperto;
ille ducem haud timidis vadentem passibus aequat.
Di, quibus imperium est animarum, umbraeque silentes
et Chaos et Phlegethon, loca nocte tacentia late,
sit mihi fas audita loqui, sit numine vestro
pandere res alta terra et caligine mersas.

This done, he promptly carries out the Sybil’s instructions.
There was a cave, deep and grim with its huge gulf
and rough, protected by the black lake and its shadows,
over which no bird could safely wing its way:
such was the breath that, pouring from its jaws,
raised itself to the dome of the heavens.
First, the priestess stood here four black-backed
bullocks, poured wine on their brows, and cutting
the topmost bristles between the horns, put them
on the holy fire as first offerings, calling aloud
on Hecate, potent both in heaven and in Erebus.
others use the knives and catch the hot blood
in dishes. Aeneas himself kills with his sword
a black-fleeced lamb for the mother of the Furies and
her great sister, and a barren cow for you, Proserpina;
next he makes a night altar to the King of the Styx
and places the complete entrails of the bulls on the
flames, pouring rich oil on the burning innards.
Look! Just as the first sun was on the point of rising,
The ground underfoot began to roar and the wooded
ridges to move, and dogs were seen howling through
the gloom at the Goddess’s arrival. “Stand away,
away, profane ones!” shouts the seer, “Leave the grove
entirely! You, Aeneas, take the path, draw your sword
from its sheath! Time for spirit and a stout heart!”
With that she plunged in fury into the open cavern;
Stepping boldly, he keeps pace with his guide. Gods
whose sway is over spirits, silent shadows, and Chaos
and Phlegethon, places hidden in the breadth of night,
may I be allowed to tell what I heard, under your auspices
to broach things buried deep in earth and darkness.