From the Aeneid, Book III, translated by Dryden
(...) Then thus replied the prophetess divine:
"O goddess-born of great Anchises' line,
The gates of hell are open night and day;
Smooth the descent, and easy is the way:
But to return, and view the cheerful skies,
In this the task and mighty labor lies.
To few great Jupiter imparts this grace,
And those of shining worth and heav'nly race.
Betwixt those regions and our upper light,
Deep forests and impenetrable night
Possess the middle space: th' infernal bounds
Cocytus, with his sable waves, surrounds.
But if so dire a love your soul invades,
As twice below to view the trembling shades;
If you so hard a toil will undertake,
As twice to pass th' innavigable lake;
Receive my counsel. In the neighb'ring grove
There stands a tree; the queen of Stygian Jove
Claims it her own; thick woods and gloomy night
Conceal the happy plant from human sight.
One bough it bears; but (wondrous to behold!)
The ductile rind and leaves of radiant gold:
This from the vulgar branches must be torn,
And to fair Proserpine the present borne,
Ere leave be giv'n to tempt the nether skies.
Homer : The Underworld,
Orphica : From man you
Plato : Ways to Hades
& The Real World
Reference address : https://www.ellopos.net/elpenor/greeks-us/virgil-underworld.asp