OSR: The Ruins and the Century Plume

The grandest city that ever lived under the earth. Masters of all they surveyed. They wanted for nothing, they feared nothing, they forgot nothing. If your setting has Atlantis, this was a colony. If your setting has an ancient fallen Snake-Man empire, this was their underground capital.

Then, one day, their city collapsed inwards. As earthquakes and fissures bent the city and dragged it down, an Archaean spire burst into the city's heart, pouring toxic smoke and boiling green clouds into the air. Thousands died immediately. Districts were sealed. Magic and long-forgotten science were desperately employed. It didn't help. The city was consumed.

Choking fumes filled the air for a full century. When they faded, the city was a jumbled ruin, an acid-scarred wreck. Rumours of vast wealth lured treasure-hunters and ambitious warlords. The damaged defenses of a long-extinct culture kept them at bay.

The Ruins are a difficult area to visit. They form a peninsula or island of danger, protected on all sides by chasms, basalt walls, and nigh-impassible terrain.

This is the high-challenge area of my underground Veins of the Earth inspired hexcrawl.

Pitor Dura

Entering the Ruins

The easiest route to the Ruins passes through one of three cave systems. There are other routes, but they involve next-to impossible climbs or the use of tunneling machines. Each one is going to be a mini-dungeon (of sorts).

11.04 - Neutral - The Obvious Trap
A dEr0-infested maze. Avoided by everyone. Inside, everything is labeled. "Do Not Touch This Lever." "This Pit Is A Trap." "This Machine Will Kill You". Some instructions were left by the dEr0. Some by desperate explorers. There are guides for hire. The guides might be dopplegangers. Some people, it is said, make it through without any permanent effects, but they would say that, wouldn't they?

11.05 - Neutral - The Blind Gloating of the Oblivion Monks
A vindicated apocalypse cult. Smug, confident. Their world ended (just as predicted), and they became rulers of the new world. Evidence to the contrary is ignored. They know no laws or moral restrictions, save that they blind their children at birth. Their sprawling monastery-fortress blocks an ancient road into the Ruins. Take up black robes and white-lead face paint and walk among them, or sneak through disused catacombs and sprawling temples. The monks will feast on your marrow if they catch you.

11.06 - Neutral - Radical Society Engine
In a brave new world! With just a handful of men! We'll start all over again! Yes, the City might be gone, but we can rebuild it. Better, even! We'll create the best system of government and the most just and stable laws. But first, we need to test our theories.  A walled system of caves. Isolated villages, accessible by secret infrastructure tunnels, hung like grapes on a vine. Villages where anyone over fifty is killed. Radical gender ratios. Drugs. Authoritarianism. Anarchy. All fed by the white nutrient paste delivered (or secretly placed) by immortal undead Overseers. Safe enough to sneak through, but don't disturb the experiments, even if they beg you to help them escape.

Gabriel Yeganyan

Inside the Ruins

The further you travel into the Ruins, the more likely you are to find astonishing treasures.

The First Layer

10.05 - Ruins - Littoral
Terrain: Brown stone spires, copper domes corroded into blue-green streaks by the Plume. Tall, narrow buildings.
Obvious Feature: Temple district, mostly looted. Smoothed statues. Ghost worshipers. Unholy relics in vaults.
Hidden Feature: Temple of Fortune occupied by Klon Fume, a radical Antling, and her band of 5 thieves. Addicted to chance.

10.06 - Ruins - Profundal
Terrain: Corroded limestone. A sludge of digested buildings.
Obvious Feature: Enormous statue with one burning eye, toppled across an entire district. Inside, 36 of Atgased's kobolds from (14.10) tunnel to seek the Eternal Flame.
Hidden Feature: Pockets of condensed deadly Plume-gas, trapped inside buildings, coated in dust. Looks just like stone.

10.07 - Ruins - Littoral
Terrain: Sandstone and marble arches. Signs of violence. Tumbled columns.
Obvious Feature: Square of Measures. Everything inside is marked by magic floating runes listing its true weight.
Hidden Feature: Waste cavern of street-cleaning automatons, full of bones, ash, chemical waste, occultum, and gold.

Shahab Alizadeh

The Second Layer

09.05 - Ruins - Littoral
Terrain: Grey-green slabs, densely tunneled. Endless identical warrens with endless barricaded doors.
Obvious Feature: Slave barracks. Giant serpent made of coiled chains and manacles and gestalt ghosts.
Hidden Feature: Obedience rods (command once per day) in sealed bunkers. Slowly warp the mind with repeated use.
 

09.06 - Ruins - Profundal
Terrain: Vertical cityscape in marble. Walls are floors. Chandeliers hang like crystal trees. Folded, crumbling.
Obvious Feature: Dvergr mining team of 5 working to crack a monolithic vault. Horrors inside. Hear them whisper.
Hidden Feature: Lake of acidic gold slurry at the bottom. Worth a fortune if condensed. Don’t fall through the mists.

09.07 - Ruins - Littoral
Terrain: Prismatic glass buildings, etched by the Plume.
Obvious Feature: Gerome Veldsbit, illusionist for hire. Wants safe passage out of the Ruins. Has gold an a secret treasure; an egg that empowers spells with uncanny life and accuracy.
Hidden Feature: Cave of eternal ice. Melts by hate only. Water made from it causes either death or ecstasy.

Nele Diel

The Third Layer

08.06 - Ruins - Littoral
Terrain: Black granite towers, heaped or decapitated.
Obvious Feature: Cave of wizard skulls parsing insane binary-click-calculations in the dark. Constant sound of teeth chattering. Cast spells if disturbed. 
Hidden Feature: Lots of black apprentice robes on dead apprentices. Minor protection from magic.

08.08 - Ruins - Littoral

Terrain: Limestone buildings, spiral-cut into lace by the Plume.
Obvious Feature: A grand dome of untouched metal. Inside, mechanisms, lenses, condensers. The Celestial Nitrogen Orrery, for monitoring the surface. See table.
Hidden Feature: Ailment transference chambers. Move diseases, mutations, etc. from one person to another.

Celestial Nitrogen Orrery

1d6	Who  You See	A Place
1	Accountants, examining ledgers.	A field
2	Pig-farmers, examining the clouds.	A meadow
3	An old woman sweeping a hut.	A moor
4	A king trying to chew a particularly difficult steak.	A village
5	A sparrow falling from a tree.	A castle
6	A young couple gathers flowers in the forest.	A heath

All things observed could be described as "churlish". If the observer has never seen the surface, they will be confused and enthralled.

07.06 - Ruins - Littoral
Terrain: Black granite cubes, tumbled, cracked open.
Obvious Feature: Forge-farms, long cooled and corroded by the Plume. Slivers of adamant and mithril remain untouched in the rust-flake layers.
Hidden Feature: Obese rust monster, too fat and happy to move. 5,000 eggs about to hatch.

07.07 - Ruins - Littoral
Terrain: Limestone palaces, warped as if by heat. Runny galleries.
Obvious Feature: One palace seems remarkably untouched, preserved in a time-locked magic field. But how to crack the field?
Hidden Feature: Ghost-caller flute in a family tomb.

06.07 - Ruins - Littoral
Terrain: Marble gardens, full of rot and chemical slime.
Obvious Feature: 3 impressively murderous dryads guarding a flash-carbonized grove. Can be distracted by fruit, vegetables. Grove contains a stone that produces pure water.
Hidden Feature: Chem-blasted tree branches are light, strong, impervious to rot. Slightly toxic.

06.08 - Ruins - Littoral
Terrain: Confusion of granite domes and stairs. Wisps of cold vapour. Rumbling, groaning.
Obvious Feature: Alchemical hydra lurking in the domes. The size of a whale. Far too many heads. Fears only sunlight.
Hidden Feature: Hydra's blood provides immunity to one or more elements. Risky.

Dark Souls - The Ringed City DLC

Ruins Random Encounter Table

Roll more frequently as you travel deeper into the Ruins.

1d20	Omen	Encounter	Page Reference
1	Gravel clatter, lime. Scrape and stomp. Muttering.	1 Gilgamash, roving on its quest. Chem-scarred, haughty. Roll for goals, etc, before the PCs see it.	VotE pg. 66
2	Creak, scrape, flap of impossible wings. Heavy, pipe-throat breath.	1d6 Gargoyles, crawling over the rubble, scanning with blind stone eyes. They hunt magic.	AD&D MM pg. 42
3	Cold air, eerie sense of being watched. Faint laughter or screams.	1d4 Ghosts, malevolent and tormented. Bound to the place they died. They fear the Plume.	AD&D MM pg. 43
4	Roar of agony, blast of lightning. Wet slow footsteps that shake the ground.	1 Storm Giant, a skinless biomechanical titan, stumbling, screaming in agony, oozing reagents.	AD&D MM pg. 45
5	Dinner plates being stacked. Thump of stone, scrape of stump-fingers on rock.	1d6 Stone Golems, ceramic, headless, trying to repair the city. Chipped armour.	AD&D MM pg. 48
6	Rust flakes in the air. Scream of torn metal, hinge-squeak march.	1 Iron Golem, armed, rusting, guarding a building or street from attack. Forged to look like a hero.	AD&D MM pg. 48
7	Shadows move oddly in the light. A faint roll of cold air.	2d10 Shadows. Baked onto walls, burnt into the ground. A deadly swarm. Safe in total darkness.	AD&D MM pg. 86
8	Scraps of conversation, grunts, a challenge. Fizz of magic.	2d6 Wights. Former inhabitants, preserved by magic. Deranged, constantly un-dying. Gas masks.	AD&D MM pg. 100
9	Rumble, shower of stone chips. Careful tapping of a hammer or pick.	5 Dvergr in a mining team. Looking for treasures, hommonculite. Not usually hostile.
10	Monosylable patter, cooing. Soft white mists. Ropes undone, flasks uncorked.	1d100 Gibberlings. Soft mist-ball 1HP ghosts, mischievous but cloying. Inconvenient. Fond of knots.
11	Buzz, static hiss. Wet pop of suction climbing gear. Purple-white light.	2d6 Squidlings, looking for treasures for their Illithid overlords. Unsettled. Good climbing gear.
12	Quiet squeaking, bickering. Hesitant footsteps. Lantern light.	5x1d10 Kobolds in a treasure-hunting party. Not hopeful for success. Willing to ally.
13	Shuffling. Faint, hoarded light. Click of metal on stone.	1d6 Volume-Folk. Recent arrivals. Generate type/activity if not already known.
14	Wisps of warm, chemical air.	City Fissure. Need to go around. Delay 1d6 hours.	-
15	Trickle of stone from above. The ground shifts.	Collapse. The floor gives way. Rocks fall. Gas rolls. 1d6 damage, delay 1d6 hours.	-
16	-	Artistic Treasure. Roll on the Treasure of the Civilopede Table.	VotE pg. 286
17	-	Precious Treasure. Roll on the Hoard Table.	-
18	-	Artifact. Roll on the Ruins Artifact table.	-
19	-	Roll on Depth Encounter Table.	-
20	-	Roll again twice on this table.	-

Tian Huaxu

1d20	Hoards
1	3d1000 copper pieces, nearly fused solid. Next to worthless.
2	3d10 silver pieces, 1 gold piece. Gold piece has a hole cut through it.
3	3d100 silver pieces, stamped with sneering faces. A strange mix of eras, rulers.
4	2d10 gold pieces, 3d10 silver pieces. Stored in black velvet bags. Polished.
5	2d10 gold pieces. Faintly stained with dried blood. One coin is soaked.
6	2d100 gold pieces. Some have been bent into half-circles. Others cut in half.
7	2d1000 gold pieces. In red paper cases of 10. Marked with an inhuman face.
8	2d10 occultum pieces in a red cloth bag. Weighs next to nothing.
9	100x1d10 gold pieces, 1d10 occultum pieces. And a small scrap of hair.
10	1d6 magic weapons (+1). 1. Sword, 2. Axe, 3. Spear, 4. Hammer, 5. Bow, 6. Dagger. Shiny.
11	1d10 silver-grey opals, shimmering. 5sp each. Coated in a thin slime.
12	1 blood-red ruby, 5gp. Always warm to the touch, but not magical.
13	Polished shells, opalescent. 10gp. Creatures from the Nightmare Sea.
14	Small bag full of diamonds. 50gp. Also contains a jeweler's eyeglass.
15	Large bag full of mixed diamonds and sapphires. 100gp. Stolen from crowns.
16	Thumb-sized diamond. 100gp. Makes a faint musical sound in the light.
17	Ivory carvings, nearly microscopic detail. 10x1d100gp. Hypnotic scenes.
18	Curse-metal bead in a lead case. 10gp. Toxic. Very very toxic.
19	Mithril ingot. 500gp. Stamped with Dvergr marks.
20	Handful of adamant nuggets. 500gp. Startlingly heavy.

1d20	Ruins Artifact
1	Master Robe. Sorcererous markings, billowing cape, tall collar. Waterproof. Amplifies spells, spell damage.
2	True Compass. Lubricated by blood (1hp/hr or use). Points to nearest example of whatever is placed inside.
3	Liquid Hydrogen Gun. Cylinders, frost. Heavy. Spays incredibly cold yet flammable liquid everywhere.
4	Occultum Extractor. Whirring drills, suction pumps. Heavy. Deposits Occultum into tiny quartz pot.
5	Miracle Fruit. As long as core is intact, regrows from nothing to full size. Infinite food. 1 ration / day / fruit.
6	Iron Lizard. Riding saddle. Fed coal, belches sparks. Like a horse that can climb on hooked fingers.
7	Defense Orb. As a Beholder, but all spells are 2d6 damage lasers. Woken by blood or magic. Semi-obedient.
8	Dimensional Chest. Inside is much bigger than the outside. Asphyxiated corpses, fleeing the Plume.
9	Sunbrella. Folded cloth spike. Unfolds to fill area with sunlight glow. Follows the cycle of the actual sun above.
10	Immaculate Collar. Gold. Wearer cannot commit any sin. They can do what they want; it's not a sin anymore.
11	Ring of Invisibility. Works on the living, not the dead.
12	Censor Staff. Erases any printed or carved writing it is aimed at. 20' range.
13	Doubling Pendant. Clutch to copy self. Copies last 1d6 hours, are indistinguishable. Only 1 copy at a time.
14	Noise Bombs. Clockwork eggs. Wind and release. Deafens in a 30' radius. Sounds horrible. Reusable.
15	Compressor. 2' cube, missing 2 top, bottom. Anything falling through shrinks to 1/2 size, keeps same weight.
16	Tubelight. Requires 1hr of cranking for 3hrs of light (as a torch). Impossible to damage.
17	Riddle of Steel. Book, fragile. Clearly and simply explains blast furnaces, metallurgy, steel manufacture.
18	Life-Leech Ring. Drain HP from people to heal. 1d6 per round. Must grapple or touch them.
19	Crown of Lies. Wearer can detect any lies spoken to it. Wearer cannot speak the truth.
20	Apocalypse Pistol. 6d6 damage, 30' line. 1d4 uses remaining. No way to tell how many uses left.