Swamp world

Swamp world
Mist rising around a bald cypress at sunrise on Caddo Lake, a cypress swamp on the Texas and Louisiana border · Shiva Shenoy, CC BY 2.0, Wikimedia Commons

A world of fiction: no known body is like it.

A planet of warm shallow water and soft ground, where the land never quite rises out of the wet and the mist never quite lifts. No known world is like this one: it steams day and night under a white sky. Pale trunks stand knee-deep like pillars, mats of floating growth hide pools deeper than a ship is long, and every step sinks. The marsh is loud with clicks, gulps and bubbles from below; when it goes quiet, something is moving. Ships that come down here rarely leave the way they planned.

Light
Dim
Going
Hard

Hear it

Hazards

  • Bottomless mire. Most of the ground is not ground: floating mats of growth over open water, mud that gives way at the second step, channels deeper than a pole. Walkers rope up, test every step and cover in a day what would take an hour elsewhere. D&D 5e (House rule): House rule: the swamp is Difficult Terrain. A creature that steps onto a hidden pool or soft mud makes a DC 12 Strength saving throw or has the Restrained condition as it sinks, up to the chest after 1 minute; a DC 12 Strength (Athletics) check, its own or a roped companion's, pulls it out. Starfinder 2e: Bogs (GM Core): shallow bogs are difficult terrain for a Medium creature and deep bogs greater difficult terrain; where a creature cannot reach the bottom, it has to Swim. Particularly extreme bogs can be hazardous terrain. Archives of Nethys
  • Marsh gas. The rotting bottom breathes out gas in slow bubbles, and in still hollows it pools unseen: a headache, a stumble, then a collapse. It burns too, and a spark at the wrong moment sets the water alight. D&D 5e (House rule): House rule: a creature without a filter mask that rests or works in a still hollow makes a DC 12 Constitution saving throw each hour; on a failure it has the Poisoned condition for 1 hour, and on a failure by 5 or more it falls Unconscious for as long. A spark there ignites the gas: each creature within 3 metres (10 feet) makes a DC 12 Dexterity saving throw, taking 2d6 Fire damage on a failure or half as much on a success. Starfinder 2e: Toxic atmosphere (GM Core): breathing poisonous gases typically deals minor poison damage (1d6 to 2d6) every minute. Archives of Nethys
  • Wet heat. Hot, and so wet that sweat never dries: by midday the air passes 38 °C and a body can no longer cool itself. Suit chillers run flat out, water goes faster than planned, and the strongest walker slows by the hour. D&D 5e: At 38 °C (100 °F) or hotter, a creature exposed without drinkable water makes a Constitution saving throw at the end of each hour, DC 5 and 1 higher each hour after, or gains 1 Exhaustion level. Medium or Heavy armour gives Disadvantage on the save; Resistance or Immunity to Fire damage passes it automatically. Starfinder 2e: Temperature (GM Core): in high humidity the heat bands start 15 °F (about 8 °C) lower. From about 27 °C it is mild heat (fatigued after 4 hours of travel); from about 32 °C, severe heat (fatigued after 4 hours and minor fire damage, 1d6 to 2d6, every hour). Archives of Nethys
  • Alien microbes. Life that never met a human: most of it cannot touch our chemistry at all, but nobody knows which of it can. Quarantine, filters and patience decide who goes home. D&D 5e (House rule): House rule: a creature that breathes the open air or eats unscanned food makes a DC 12 Constitution saving throw at the end of the day; on a failure it has the Poisoned condition for 1d4 days. A creature that succeeds three days in a row is safe from this world's microbes.
  • Food that is not food. The fruit looks ripe, the fish looks fat, and none of it may be made of anything a human body can use. Some of it is poison; most of it simply does not feed. D&D 5e (House rule): House rule: foraging finds no food a human can live on unless a lab or a DC 18 Intelligence (Nature) check proves it. Living on it otherwise is Malnutrition: a creature that eats less than half its daily food makes a DC 10 Constitution save at the end of the day or gains 1 Exhaustion level.

What may happen

  1. The sun is a pale disc behind the haze; the light seems to come from everywhere, and nothing casts a shadow.
  2. Bubbles rise in a long line across the pool, as if something were walking along the bottom.
  3. The green ground ahead gives a little under the probe pole: it is a floating mat, and the pole finds no bottom.
  4. A crashed lander sits tilted in the water up to its windows, its hatch open and its cabin full of black water.
  5. Inside the wreck, the dry upper deck has been lived in: a bedroll, empty ration packs, and tally marks scratched on the wall.
  6. At dusk the marsh fills with clicking, millions of voices rising and falling in waves that sweep across the water.
  7. Twice in an hour, the ripple of something large slides along beside the party's line of march, keeping pace.
  8. The only dry hummock for kilometres has a ring of sharpened stakes around it, old and rotten.
  9. Steam rises from a crack in the mud with a slow sigh, and the water around it is too hot to touch.
  10. The probe pole snaps in someone's hands: something below has bitten through it.
  11. Where the party has waded, the water glows faintly green for a minute, a trail of light behind them.
  12. A wall of stiff reeds three metres high, edged like saws, blocks the way as far as can be seen.
  13. A cluster of clear eggs, each the size of a fist, clings to a trunk just above the water; inside, something turns.
  14. A red flare climbs into the haze a few kilometres east and hangs there, blurred, before fading.
  15. A forest of dead trunks stands grey in still water, each one ringed with white crust at the waterline.
  16. Small flat swimmers leap from the pool all at once and patter back onto the water like rain.
  17. Warm water has seeped into someone's boot through a seam, and the foot inside has gone white and wrinkled.
  18. A marker pole stands in the water with a strip of faded reflective tape tied to it; another stands a hundred metres further on.
  19. A raft of lashed tubes and hull plating floats against the reeds, empty, with a paddle still tied to it.
  20. All night, something heavy splashes now and then out in the dark water, never close, never far.
  21. Bag-shaped nests of woven fibre hang over the channel, and the closest one is humming.
  22. A cargo crate from the wreck has drifted onto a mud bank, its seals intact and its manifest label still readable.
  23. In the morning the boat's mooring line has been chewed through, and the boat has drifted out of reach.
  24. One pool is clear as glass, and on its sandy bottom lie hundreds of coiled shells, all turned the same way.
  25. Long-toed, webbed prints lead out of the water and up to the camp's fence, then back.

Adventure hooks

  1. An insurer offers a share of the cargo to whoever finds the lander that went down in the marsh, and so does the crew that sank it.
  2. A survey team's marker poles lead into the swamp and stop in the middle of open water.
  3. A settler family on the only rock for a hundred kilometres refuses to be evacuated and will not say what keeps them there.
  4. Something in the marsh has learned to imitate a distress call, and it is getting better at it.

Who and what is met

Each is an SRD stat block under another name, as game masters reskin them.

Other worlds

Cold desert world, Ice moon with a hidden ocean, Methane world, Hothouse world, Volcanic world, Airless world, Ocean world, Tidally locked world, Earthlike world, Acid world, Jungle world

This work includes material from the System Reference Document 5.2.1 ("SRD 5.2.1") by Wizards of the Coast LLC, available at https://www.dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License, available at https://creativecommons.org/licenses/by/4.0/legalcode.

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