Dungeon Master's Guide

In subterranean settlements, even races that have
darkvision use fire for warmth, cooking, and defense.
But many creatures have no need of warmth or light.
Adventurers must bring their own sources of light into
usty tombs where only undead stand guard, abandoned
;uins teeming with predatory monsters and oozes, and
natural caverns where sightless creatures hunt.
The light of a torch or lantern helps a character
: e over a short distance, but other creatures can
: e that light source from far away. Bright light in an
environment of total darkness can be visible for miles,
j]ough a clear line of sight over such a distance is rare
underground. Even so, adventurers using light sources
JJ a dungeon often attract monsters, just as dungeon
•eatures that shed light (from phosphorescent fungi
-o the glow of magical portals) can draw adventurers'
anention.
_UR QUALITY
ubterranean tunnels and aboveground ruins are often
enclosed spaces with little airflow. Though it's rare for
a dungeon to be sealed so tightly that adventurers have
ouble breathing, the atmosphere is often stifling and
oppressive. What's more, odors linger in a dungeon and
can be magnified by the stillness of the atmosphere.
OUNDS
A dungeon's enclosed geography helps channel sound.
The groaning creak of an opening door can echo down
hundreds of feet of passageway. Louder·noises such
a the clanging hammers of a forge or the din of battle
can reverberate through an entire dungeon. Many
creatures that live underground use such sounds as a
"';'\ay of locating prey, or go on alert at any sound of an
adventuring party's intrusion.
DUNGEON HAZARDS
The hazards described here are but a few examples of
the environmental dangers found underground and in
other dark places. Dungeon hazards are functionally
imilar to traps, which are described at the end of
this chapter.
Detecting a Hazard. No ability check is required
to spot a hazard unless it is hidden. A hazard that
resembles something benign, such as a patch of slime
or mold, can be correctly identified with a successful
Intelligence (Nature) check. Use the guidelines in
chapter 8 to set an appropriate DC for any check made
to s pot or recognize a hazard.
Hazard Severity. To determine a hazard's deadliness
relative to the characters, think of the hazard as a trap
and compare the damage it deals with the party's level
using the Damage Severity by Level table later in the
chapter (the table also appears in chapter 8).
BROWN MOLD
Brown mold feeds on warmth, drawing heat from
anything around it. A patch of brown mold typically
covers a 10-foot square, and the temperature within 30
feet of it is always frigid.
When a creature moves to within 5 feet of the mold
for the first time on a turn or starts its turn there, it
must make a DC 12 Constitution saving throw, taking
22 (4d10) cold damage on a failed save, or half as much
damage on a successful one.
Brown mold is immune to fire, and any source of fire
brought within 5 feet of a patch causes it to instantly
expand outward in the direction of the fire, covering a
10-foot-square area (with the source of the fire at the
center of that area). A patch of brown mold exposed to
an effect that deals cold damage is instantly destroyed.
GREEN SLIME
This acidic slime devours flesh , organic material, and
metal on contact. Bright green, wet, and sticky, it clings
to walls, floors, and ceilings in patches.
A patch of green slime covers a 5-foot square, has
blindsight out to a range of 30 feet, and drops from
walls and ceilings when it detects movement below it.
Beyond that, it has no ability to move. A creature aware
of the slime's presence can avoid being struck by it with
a successful DC 10 Dexterity saving throw. Otherwise,
the slime can't be avoided as it drops.
A creature that comes into contact with green slime
takes 5 (1d10) acid damage. The creature takes the
damage again at the start of each of its turns until the
slime is scraped off or destroyed. Against wood or
metal, green slime deals 11 (2d10) acid damage each
round, and any nonmagical wood or metal weapon or
tool used to scrape off the slime is effectively destroyed.
Sunlight, any effect that cures disease, and any effect
that deals cold, fire, or radiant damage destroys a patch
of green slime.
WEBS
Giant spiders weave thick, sticky webs across passages
and at the bottom of pits to snare prey. These web-filled
areas are difficult terrain. Moreover, a creature entering
a webbed area for the first time on a turn or starting its
turn there must succeed on a DC 12 Dexterity saving
throw or become restrained by the webs. A restrained
creature can use its action to try to escape, doing
so with a successful DC 12 Strength (Athletics) or
Dexterity (Acrobatics) check.
Each 10-foot cube of giant webs has AC 10, 15
hit points, vulnerability to fire, and immunity to
bludgeoning, piercing, and psychic damage.
YELLOW MOLD
Yellow mold grows in dark places, and one patch covers
a 5-foot square. If touched, the mold ejects a cloud of
spores that fills a 10-foot cube originating from the
mold. Any creature in the area must succeed on a DC
15 Constitution saving throw or take 11 (2d10) poison
damage and become poisoned for 1 minute. While
poisoned in this way, the creature takes 5 (1d10) poison
damage at the start of each of its turns. The creature
can repeat the saving throw at the end of each of its
turns, ending the effect on itself on a successful save.
Sunlight or any amount of fire damage instantly
destroys one patch of yellow mold.
CHAPTER 5 I ADVENTURE ENVIRONMENTS
105