From The Carrion Throne, which is probably one of the most Grimdark works in all of 40K Fiction:
"Terra.
Holy Terra, marvel of the galaxy, heart of wonder. No jewel shone more brightly, no canker was more foul. At its nexus met the fears and glories of a species, rammed tight within the spires and the vaults, the pits and the hab-warrens. Spoil-grey, scored and crusted with the contamination and majesty of ten long millennia, a shrine world that glowed with a billion fires, a tomb that clutched its buried souls close. All the planet's natural beauty had long since been scrubbed from its face, replaced by the layers upon layers of a single, creeping hyper-city. The sprawl blotted out the oncegreat oceans and the long-hewn forests under suffocating mountains of rockcrete and plasteel, tangled and decaying and renewed and rebuilt until the accretions stretched unbroken from the deepest chasms to the exalted heights.
No part of that world was free of the hand of ma. Viewed from space, the planet's night-shrouded hemisphere glittered with constellations of neon and sulphur, while its sunlit hemisphere gasped in a hot haze of pale grey. Its skies were clogged with voidcraft and lifters, packed with the manufactures and commodities that kept the teeming world from starving itself. With those commodities came living bodies ― pilgrims by the million, products of a migration that never ended, bringing souls from across the vastness of space whose only wish was to live long enough to reach the sacred precincts of the Palace itself; to somehow endure the crowds and the hardship and the myriad predators that circled them for just one glimpse, even the smallest, of the golden towers portrayed in the Ecclesiarchy vidpicts, before they died in rapture.
So few made it. Most died on the warp journey, either of old age or through the loss of their ships in the void. Those who reached the solar system waited for years in the processing pens on Luna, then the vast orbital stations within sight of the planet below. It was said that a man could be born, live and die within those cavernous holding centres, all while his documentation worked its way tortuously through the offices of scribes and under-scribes. Often it would be lost, sometimes stolen, a mere speck amid the avalanche of parchment folios that fuelled the administrative machinery of the Imperium's sclerotic heart.
And yet, those few who by luck or the will of the Emperor made it to the sacred soils of humanity's birthworld still numbered in the millions, such was the fecundity of the eternal pilgrimage. Like the forgotten tides of Old Earth, the flow waxed and waned, governed by the great festivals of the Ministorum, the feasts of the saints and the Lords of Terra. And of all the sacred days ordained for the masses to partake in, by far the most sacred was the remembrance of the Angel ― Sanguinala, the Red Feast, the Festival of the Blessed Sacrifice. On that day, once every solar year, the numbers swelled beyond reason, and the pilgrims crammed like cattle into the feeder stations, clawing at the gates and screaming at the guards to let them in. The most exalted of all, so they said, would be permitted to approach the Eternity Gate itself, to witness the rites of remembrance performed on the site of the Angel's legendary stand as the feast reached its frenetic climax."
"Spinoza looked out of the nearside portal. The airspace around them was thick with boiling toxspirals, twisting up from the cityscape below. The shuttle pushed up into regulated airspace ― the preserve of Adeptus Arbites, the Inquisition and other exempted Imperial agents ― and the craft's macro-turbines opened up.
Below them, a thousand lesser aircraft plied filth-trailed passages from spire to spire, feeding the gritty haze that shrouded the depths below. Marker-lumens, red and filmy, blinked by the million, faint beacons amid a sea of perpetual murk.
Above them, just visible against the bone-grey of the sky, were the shadows of the sentinel watchstations, hanging in low orbit, each crammed with listening devices and augur batteries, forever scanning. Above them in turn were the behemoths of the defence grid, some as old as the Imperium itself, and above them, out into the icy vacuum, were the voidships ― millions of them, embarking, arriving or engaged in ceaseless patrols.
Spinoza had served with Tur on major hive worlds, but the multitudes here were still numbing. She looked down, watching the airborne fleets mingle and congest, and knowing that below, far below, groundcars and grav-transits were crawling through stacked-deep tunnels and catacombs, ferrying far more souls than could ever hope to afford privileged above-ground passage. She also knew that what she witnessed was the same on every single square kilometre of the world's surface ― there were no forests, no seas, just an unbroken press of spires, hab towers, temples, gaols, crypts and garrisons, grasping and throttling the entire globe in a vice of iron and rockcrete."
"Making the leap from solid earth and into the void beyond had once been beyond the dreams of the insane. Generations of soil-dwellers, scratching about amid the dirt of aeons, prisoners of gravity, had looked up at the stars and called them gods, knowing that they would forever be far out of reach.
No longer. Though so much else had been forgotten, the means to break the bonds of the planetary was still commonplace within the Imperium, so much so that even a modestly endowed mercantile combine would have a dozen system-runners in its orbital sheds, plying the short hop between terrestrial landing stages and local orbit, ready to rendezvous with the true giants of the deep. The atmosphere of the Throneworld was nigh as congested as its urban surfaces, scored and re-scored by the crossover trails of a million near-space vessels. There had ceased to be much significant difference between the atmospheric and the true-vacuum zones ― they were just steadily rarefied sections of the same world-city, extending up from the darkest chasms, out beyond the turrets and into the high-air stations, and then further out, back into darkness, up to where the mighty orbital plates slowly gyrated in the harsh light of an unfiltered su.
A vessel blasted off from a sanctioned landing site on Terra every millisecond, so they said. Another landed to take its place not long after. They arrived full, they left empty. The Throneworld did not trade with the rest of the Imperium ― it consumed it. Goods were sucked in from every corner of every segmentum, dragged out from the holds of the leviathans that carried them, seized by the ravenous populace and devoured, and it was never enough. A million cargo-lifters might touch down in a single hour, and still thousands would starve. Any delay in the endless circular passage, and tens of thousands would die. Like a hopeless opiate addict, the populace could never be satisfied, never given enough. The birthplace of humanity now squatted like some obscene, famished infant at the heart of its web of stellar kingdoms, ingesting the last dregs of energy out of the straggling fringes and gulping them down into greedy oblivion."
"With the toxic rad-zone behind them, the stars at last came out ― a dazzling belt of rawlight strewn across the velvet darkness. After so long down in the grime, seeing that purity nearly made Spinoza cry out loud. This was the element she loved, where war could be conducted in the open, in the vaults of the heavens where the fires wheeled.
Except this was not empty space. Over to their left, the vast curve of an orbital plate gently turned, its withered grey armour stretching off into darkness. Defence stations loomed further up, each the size of cities, studded with gape-mawed novacannons and graviton world-enders. A colossal grand cruiser bearing the livery of Battlefleet Solar crawled off into the middle distance, escorted by wings of frigates. Between those giants swam shoals of lesser craft ― fleet tenders, guide-tugs, the hundreds of orbital lifters, all of them fat and clumsy, riding on dull red cushions of plasma-glow."
"They climbed higher, and the horizon fell away, curving at the edges. The sun, for so long weak, became a yellow-white hole in the void, brilliant and dazzling. More defence stations swam into view, antique monsters, floating like castles in the void, their walls still blackened from munitions fired ten thousand years ago. Truly massive voidships lurked on the edge of sensor range, far too huge to enter the patrolled orbital zone and attended to by flocks of scurrying lifters. They were virtually invisible, those giants, hulking out in the frigid wastes, their scale only given away by flickering marker lights in the deep.
'Coming into augur-margins, now,' reported Aneela, steering the Spiderwidow under the shadow of a defence cluster and out past the gravity distortion of a second orbital plate. 'Do you wish me to run silent?'"