Fungal Mine

Mushrooms as tall as trees, caps the width of a house, and spores hanging in the air like dust in a barn. The forest breathes: at dawn it puffs out clouds, at dusk it draws them back. Shafts and galleries dug by people after ore, coal, salt or stone. Dark, cramped and dangerous, with bad air, flooding and falling rock, and the work of generations in its walls.

Hear it

Fungal: Underground Mushroom Forest (In the album RPG Ambiences Vol. 3)
Fungal: Breathing Mushroom Forest (In the album RPG Ambiences Vol. 7)
At night: Breathing Mushroom Forest at Night (On Patreon, Guardian tier)
In the woods: Mushroom Forest (In the album RPG Ambiences Vol. 3)
At work: Active Mine (In the album RPG Ambiences Vol. 3)
A mine cart: Slow Minecart in Mine Layer (On Patreon, Raven tier)
The shaft: Mineshaft Elevator (On Patreon, Raven tier)
A collapse: Collapsing Mine (In the album RPG Ambiences Vol. 7)
Darkness: Gloomy Cave (In the album RPG Ambiences Vol. 1)
Bad air: Mineshaft Elevator in Damp Cave (On Patreon, Raven tier)
Rising water: Underground Waterfall (In the album RPG Ambiences Vol. 7)

For the table

Ground: hard going, about 10 km a day on foot
Water: by season
Foraging: poor

Hazards

Darkness. No daylight at all: every step needs a light, and every light burns out. A party without spare torches or oil is blind.
Bad air. Low pockets of foul or burning air: lamps gutter, then miners faint. Miners carried a flame, later a bird, to tell.
Falling rock. Frost, rain or a careless step bring stones down from above. Scree slides underfoot.
Rising water. Rain outside fills passages within hours. A way in can become a sump.
Spore cloud. A stepped-on cap bursts in a yellow cloud. It burns the throat and the eyes, and the cough lasts for days.
Sleeping spores. At dusk the forest breathes out a sweet haze. It is very easy to sit down for a moment, and very hard to get up.
Rotten floor. The ground is a crust of mycelium over soft rot. It holds a man, then one day it does not.

D&D 5e

Plays as: Underdark, normal pace at most
Checks: forage: Survival DC 20 · find the way: DC 10 · search: DC 20
Creatures are spotted at: 2d6 × 10 ft

Darkness. Darkness is Heavily Obscured: a creature trying to see into it is Blinded. Dim light is Lightly Obscured. Darkvision turns darkness into dim light within its range, in shades of grey.
Bad air. A creature that cannot breathe holds its breath for 1 + its Constitution modifier minutes (at least 30 seconds), then gains 1 Exhaustion at the end of each of its turns until it breathes again; that Exhaustion goes once it does.
Spore cloud. (House rule) Creatures within 10 feet make a DC 12 Constitution save or have the Poisoned condition for 1 hour. A wet cloth over the face gives Advantage.
Sleeping spores. (House rule) A creature that stops in the haze makes a DC 13 Constitution save or falls asleep (Unconscious) for 1 hour; damage or a companion's action wakes it. Those who sleep there wake with 1 Exhaustion.
Rotten floor. (House rule) The first creature to cross a weak spot makes a DC 12 Dexterity save or falls 10 feet into the rot, taking 1d6 bludgeoning damage and the Poisoned condition until it climbs out and washes.

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.

Pathfinder Second Edition

Plays as (Pathfinder Second Edition): underground, difficult terrain, about 16 km a day at Speed 25
Checks: Subsist: Survival DC 40 · Sense Direction: Survival DC 20

Falling rock. An avalanche, landslide or collapse deals major or massive bludgeoning damage (8d6 to 24d6); a Reflex success halves it and a critical success also avoids burial. Buried creatures take minor damage each minute and are dug out with Athletics (GM Core p. 96).

This product is licensed under the ORC License located at the Library of Congress at TX 9-307-067 and available online at various locations including paizo.com/orclicense, azoralaw.com/orclicense, and others. All warranties are disclaimed as set forth therein. Attribution: this rules layer is based on the following Licensed Material: Pathfinder Player Core © 2023 Paizo Inc., Designed by Logan Bonner, Jason Bulmahn, Stephen Radney-MacFarland, and Mark Seifter. Authors: Alexander Augunas, Kate Baker, Logan Bonner, Jason Bulmahn, Carlos Cabrera, Calder CaDavid, James Case, Eleanor Ferron, Steven Hammond, Joan Hong, Vanessa Hoskins, James Jacobs, Jenny Jarzabski, Erik Keith, Dustin Knight, Lyz Liddell, Luis Loza, Patchen Mortimer, Dennis Muldoon, Stephen Radney-MacFarland, Mikhail Rekun, David N. Ross, Michael Sayre, Mark Seifter, Kendra Leigh Speedling, Mark Thompson, Clark Valentine, Andrew White, Landon Winkler, and Linda Zayas-Palmer; Pathfinder GM Core © 2023 Paizo Inc., Designed by Logan Bonner and Mark Seifter. Authors: Amirali Attar Olyaee, Logan Bonner, Creighton Broadhurst, Jason Bulmahn, James Case, Jesse Decker, Eleanor Ferron, Fabby Garza Marroquín, Jaym Gates, Matthew Goetz, James Jacobs, Brian R. James, Jenny Jarzabski, Dustin Knight, Jason LeMaitre, Lyz Liddell, Luis Loza, Ron Lundeen, Stephen Radney-MacFarland, David N. Ross, Michael Sayre, Mark Seifter, Owen K.C. Stephens, Amber Stewart, Clark Valentine, Landon Winkler, and Linda Zayas-Palmer; Pathfinder Monster Core © 2024 Paizo Inc., Authors: Alexander Augunas, Dennis Baker, Kate Baker, Joshua Birdsong, Joseph Blomquist, Logan Bonner, Jason Bulmahn, James Case, John Compton, Paris Crenshaw, Adam Daigle, Darrin Drader, Brian Duckwitz, Robert N. Emerson, Scott Fernandez, Eleanor Ferron, Leo Glass, Matthew Goodall, BJ Hensley, Thurston Hillman, Vanessa Hoskins, James Jacobs, Jenny Jarzabski, Miko Kallio, Jason Keeley, Jeff Lee, Lyz Liddell, Luis Loza, Ron Lundeen, Robert G. McCreary, Philippe-Antoine Menard, Jacob W. Michaels, Dave Nelson, Jason Nelson, Tim Nightengale, Stephen Radney-MacFarland, Mikhail Rekun, Patrick Renie, Alex Riggs, David N. Ross, Michael Sayre, Mark Seifter, Chris S. Sims, Amber Stewart, Jeffrey Swank, William Thompson, Jason Tondro, Clark Valentine, Landon Winkler, Tonya Woldridge, and Linda Zayas-Palmer. If you use our Licensed Material in your own published work, please credit us as follows: Biomes, Pathfinder Second Edition rules layer © 2026 Michael Ghelfi. Reserved Material: the names of Biomes and its catalogues, its descriptions, sounds, art and code. Pathfinder is a registered trademark of Paizo Inc.; this site is not published, endorsed, or specifically approved by Paizo Inc.

Adventure hooks

A brewer wants spores from one particular giant mushroom for an ale that the whole county will want. The mushroom breathes out a sleeping cloud every dawn, and the last two collectors are still asleep beneath it.
The fungi are spreading into the village, through cellars and into the bread. The miller says they are harmless; the miller is the only one who has eaten the bread and seems happier than ever.
A scholar believes the whole fungal growth is a single living thing, and wants to talk to it. She has worked out how, and needs someone to stand very still in a spore cloud for an hour.
A lost party of soldiers has been living under the giant caps for a year, growing pale and gentle. Their commander wants them back; they want to be left alone, and the mushrooms seem to agree.
The miners have broken into a gallery nobody dug, its walls smoothed by tools, its floor worn by feet. The owner wants it explored before the men refuse to go back down.
The owner has stopped paying, claiming the vein is worked out. The miners know it is not, and they know he walled up the richest galleries after the collapse, with two of their friends still behind the wall.
A retired miner, nearly blind, wants to go down once more to the place where he first struck the vein. He will find the way only by the sound of the water, and he wants company, not help.
The miners leave bread for the little folk of the mine so they will knock before a roof falls. The new foreman stopped the custom to save money, and now the knocking never stops, at any hour, everywhere.

Creatures

Shrieker Fungus (harmless, Challenge 0)
Violet Fungus (a threat to the unwary, Challenge 1/4)

Also met here

Giant Fire Beetle (harmless, Challenge 0)
Rust Monster (a threat to the unwary, Challenge 1/2)
Xorn (a fight to fear, Challenge 5)

To gather

Mycelium

The same milieu, otherwise

Mine, Corrupted Mine, Haunted Mine, Crystalline Mine, Dead Mine, Eldritch Mine, Toxic Mine, Burning Mine

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