Here's an exceprt from Olympos, a rather disappointing, mildly insulting, and only occasionally amusing novel written by Dan Simmons. This particular chapter depicts the Red Prison rather well, though. I like seeing the planes, particularly lower ones, so disproportional and unhospitable by human standards.
First of all, Achilles can’t quite breathe the air here. While the quantum singularity of his Fate to Die by Paris’s Hand theoretically protects him from death, it doesn’t protect him from rasping, wheezing, and collapsing on the lava-hot black stone as the methane-tainted air fouls and scours his lungs. It’s as if he’s trying to breathe acid.
Secondly, this Tartarus is a nasty place. The terrible air pressure - equivalent to two hundred feet beneath the surface of Earth’s sea - presses in on every square inch of Achilles’ aching body. The heat is terrible. It would have long since killed any merely mortal man, even a hero such as Diomedes or Odysseus, but even demi-god Achilles is suffering, his skin blotched red and white, boils and blisters appearing everywhere on his exposed flesh.
Finally, he is blind and almost deaf. There is a vague reddish glow, but not enough to see by. The pressure here is so great, the atmosphere and cloud cover so thick, that even the small illumination from the pervasive volcanic red gloom is defeated by the rippling atmosphere, by fumes from live volcanic vents, and by the constant curtain-fall of acid rain. The thick, superheated atmosphere presses in on the fleet-footed mankiller’s eardrums until the sounds he can make out all seem like great, muted drumbeats and massive footsteps - heavy throbs to match the throbbing of his pressure-squeezed skull.
Achilles reaches under his leather armor and touches the small mechanical beacon that Hephaestus had given him. He can feel it pulse. At least it hasn’t imploded from the terrible pressure that presses in on Achilles’ eardrums and eyes.
Sometimes in the terrible gloom, Achilles can sense movement of large shapes, but even when the volcanic glow is at its reddest, he can’t make out who or what is passing near him in the terrible night. He senses that the shapes are far too big and too oddly shaped to be human. Whatever they are, the things have ignored him so far.
Fleet-footed Achilles, son of Peleus, leader of the Myrmidons and noblest hero of the Trojan War, demigod in his terrible wrath, lies spread-eagled flat on a pulsing-hot volcanic boulder, blinded and deafened, and uses all of his energy just to keep breathing.
Perhaps, he thinks, I should have come up with a different plan for defeating Zeus and bringing my beloved Penthesilea back to life.
Even the briefest thought of Penthesilea makes him want to weep like a child - but not an Achilles’ child, for the young Achilles had never wept. Not once. The centaur Chiron had taught him how to avoid responding to his emotions - other than anger, rage, jealousy, hunger, thirst, and sex, of course, for those were important in a warrior’s life - but weep for love? The idea would have made the Noble Chiron bark his harsh centaur’s laugh and then hit young Achilles hard with his massive teaching stick. “Love is nothing but lust misspelled,” Chiron would have said - and struck seven-year-old Achilles again, hard, on the temple.
What makes Achilles want to weep all the more here in this unbreathable hell is that he knows somewhere deep behind his surging emotions that he doesn’t give a damn about the dead Amazon twat - she’d come at him with a fucking poisoned spear, for the gods’ sake - and normally his only regret would be that it took so long for the bitch and her horse to die. But here he is, suffering this hell and taking on Father Zeus himself just to get the woman reborn - all because of some chemicals that gash-goddess Aphrodite had poured on the smelly Amazon.
Three huge forms loom out of the fog. They are close enough that Achilles’ straining, tear-filled eyes can make out that they are women - if women grew thirty feet tall, each with tits bigger than his torso. They are naked but painted in many bright colors, visible even through the red filter of this volcanic gloom. Their faces are long and unbelievably ugly. Their hair is either writhing like snakes in the superheated air or is a tangle of serpents. Their voices are distinct only because the booming syllables are unbearably louder than the booming background noise.
“Sister Ione,” booms the first shape looming over him in the gloom, “canst thou tell what form this is spread-eagled across this rock like a starfish?”
“Sister Asia,” answers the second huge form, “I wouldst say it were a mortal man, if mortals could come to this place or survive here, which they cannot. And if I could see it were a man, which I cannot since it lieth upon its belly. It does have pretty hair.”
“Sister Oceanids,” says the third form, “let us see the gender of this starfish.”
A huge hand roughly grips Achilles and rolls him over. Fingers the size of his thighs pluck away his armor, rip off his belt, and roll down his loin cloth.
“Is it male?” asks the first shape, the one her sister had called Asia.
“If you wouldst call it so for so little to show,” says the third shape.
“Whatever it is, it lies fallen and vanquished,” says the female giant called Ione.
Suddenly large shapes in the gloom that Achilles had assumed were looming crags stir, sway, and echo in non-human voices, “Lies fallen and vanquished!”
And invisible voices farther away in the reddish night echo again, “Lies fallen and vanquished!”
The names finally click. Chiron had taught young Achilles his mythology, as well as his theology to honor the living and present gods. Asia and Ione had been Oceanids - daughters of Okeanos - along with their third sister Panthea… the second generation of Titans born after the original mating of Earth and Gaia, Titans who had ruled the heavens and the earth along with Gaia in the ancient times before their third-generation offspring, Zeus, defeated them and cast them all down into Tartarus. Only Okeanos, of all the Titans, had been allowed exile in a kinder, gentler place - locked away in a dimension layer under the quantum sheath of Ilium-Earth. Okeanos could be visited by the gods, but his offspring had been banished to stinking Tartarus: Asia, Ione, Panthea, and all the other Titans, including Okeanos’ brother Kronos who became Zeus’s father, Okeanos’ sister Rhea who became Zeus’s mother, and Okeanos’ three daughters. All the other male offspring from the mating of Earth and Gaia - Koios, Krios, Hyperion, and Iapetos, as well as the other daughters - Theia, Themis, Mnemosyne, golden-wreathed Phoebe, and sweet Tethys - had also been banished here to Tartarus after Zeus’s victory on Olympos thousands of years earlier.
All this Achilles remembers from his lessons at the hoof of Chiron. A fucking lot of good it does me, he thinks.
“Does it speak?” booms Panthea, sounding startled.
“It squeaks,” says Ione.
All three of the giant Oceanids lean closer to listen to Achilles’ attempts at communication. Every attempt is terribly painful for the mankiller, since it means breathing in and trying to use the noxious atmosphere. An observer would have guessed from the resulting sounds - and guessed correctly - that there is an unusual amount of helium remaining in the carbon dioxide, methane, ammonia mix of Tartarus’ soup-thick atmosphere.
“It soundeth like a mouse that hath been squashed flat,” laughs Asia.
“But the squeaks sound vaguely like a squashed mouse’s attempt at civilized language,” booms Ione.
“With a terrible dialect,” agrees Panthea.
“We need to take him to the Demogorgon,” says Asia, looming closer.
Two huge hands roughly lift Achilles, the giant fingers squeezing most of the ammonia, methane, carbon dioxide, and helium out of his aching lungs. Now the hero of the Argives is gaping and gasping like a fish out of water.
“The Demogorgon will want to see this strange creature,” agrees Ione. “Carry him, Sister, carry him to the Demogorgon.”
“Carry him to the Demogorgon!” echo the giant, insectoid shapes following the three giant women.
“Carry him to the Demogorgon!” echo larger, less familiar shapes following farther behind.
I do like the portrayal of the Oceanids.
There was a pretty good description of Agathys in Larry Niven and Jerry Pournelle's book Inferno, which was based closely on Dante's work of the same name.
The heroes are two petitioners attempting to escape from Dante's Hell.
Benito was standing. "That will not help. Nothing helps," he said patiently. "You must bear the cold."
If he could do it...I stood up and closed my eyes tight against the soft, unreasonably cold breaze. Surely it was below freezing, way below freezing. How cold was it? If it could kill a man in minutes, or seconds, I'd never know it. I couldn't die.
"Benito? Burst into flame again for your good friend."
"I would if I could. My apologies, Allen." Benito took my arm. We walked.
It had certainly been worth asking.
Was it water ice we walked on? For all of me, it could have been dry ice, or frozen nitrogen, or something even colder.
I kicked something that cursed me without emotion. I tried to open my eyes. The wind's tears had frozen them shut. I pulled them open, painfully, with my fingers.
"Leave them open," Benito said without pity, "and they will freeze open."
When the urge came to blink I fought it. Then there was no need, for my eyes would not close. I looked at what I'd kicked. I said, "Sorry."
[Here the wanderers have a brief discussion with two petitioners frozen in the ice except for their heads]
We walked with care, to avoid kicking heads. There were certainly enough of them. But now it was worse; here the dead had been buried supine , and so we would have been stepping on faces.
Once I missed my step and came down hard on a human face. The ice across its eyes crackled under my fet, and I leapt back fast. "Sorry!"
"Thanks," I heard.
"Mistake."
"Thanks, oh, thanks," it said, weeping. "I haven't cried in years. The damned ice froze across my eyes, and I couldn't cry. Thanks."
I felt awful. This was an awful place. "That's okay," I said. I bent and picked the remaining shards of ice from her eyes. "What'd you do?"
"I don't want to say."
"Okay."
I tore the ice visors from a couple of dozen pairs of eyes. Always they froze over again almost immediately. Only one ever said "Thanks." Finally I gave it up. There were just too many.
[Here there is a discussion with a succession of further petitioners, the spirits of Al Capone and Jesse James]
Suddenly there were no more heads. There was only the ice, and the wind that had blown the others away. We leaned into it and kept moving.
I said, "Hell has run out of sins?"
"Look down."
Hell had not run out of sinners. They were buried beneath the ice in weird positions. Once I looked down, and then no more.
We walked crouched, wrapped in our own arms, to no purpose. The wind had early sucked every erg of heat out of us.
I saw motion ahead, high up.
As we drew near a shadowy mass loomed around the suggestion of motion. Pterodactyls on a mountain? Restless, rhythmic motion, like the wings of enormous birds. And gradually it all came clear.
There was a humanoid form, a hairy torso more than a mile tall. We stood at the bottom, at waist level, and looked up at three vast faces whose features were almost lost in the distance. Bat wings flapped on either side of each face, and the wind was now beating down at our heads.