Environment & Hazards
Terrain and environmental conditions are as dangerous as any monster. This chapter covers universal hazards, wilderness terrain, dungeon features, weather, urban adventures, and the sample hazards and disasters from the Game Mastery Guide.
Universal Environmental Hazards
The following hazards apply in any terrain. Terrain-specific hazards (forest fire, avalanche, etc.) are listed under their terrain type.
Acid Effects
- Contact / splash: 1d6 acid damage per round of exposure
- Total immersion (e.g. vat): 10d6 per round
- Fumes (adjacent to large body): Fortitude DC 13 or 1 Con damage per round; ends when creature moves away
- Creatures immune to acid can still drown if fully immersed — apply drowning rules normally
Cold Dangers
| Temperature | Check | Frequency | Failure |
|---|---|---|---|
| Cold (below 40 °F) | Fort DC 15 (+1/prev) | 1/hour | 1d6 nonlethal damage |
| Severe cold (below 0 °F) | Fort DC 15 (+1/prev) | 1/10 min | 1d6 nonlethal damage |
| Extreme cold (below −20 °F) | Fort DC 15 (+1/prev) | 1/min | 1d6 lethal + 1d4 nonlethal (no save for lethal) |
Any nonlethal damage from cold causes frostbite / hypothermia (fatigued). Penalties end when the nonlethal damage is recovered. Characters in a cold weather outfit check once per hour for cold and severe cold (not more frequently).
A Survival check (see skill description) can provide a bonus on these saves and extend it to nearby allies.
Darkness
Creatures blinded by darkness (lacking darkvision) suffer the following penalties:
- 50% miss chance (total concealment on all foes)
- Must pinpoint foe's location before attacking correct square
- Lose Dex bonus to AC (if positive); –2 penalty to AC
- –4 penalty on Perception checks and most Str/Dex skills
- Cannot run or charge; DC 10 Acrobatics to move faster than half speed
- Cannot use gaze attacks; immune to gaze attacks
- No precision damage (sneak attack, etc.)
- Free Perception check each round to locate unseen foes (DC = their Stealth)
Falling
- Normal fall: 1d6 damage per 10 ft fallen, max 20d6; creature lands prone
- Deliberate jump: first 1d6 is nonlethal
- Successful DC 15 Acrobatics: no damage from first 10 ft; second 10 ft deals nonlethal instead of lethal
- Yielding surface (soft ground, mud): first 1d6 converted to nonlethal (cumulative with above)
- Casting while falling: requires concentration check DC 20 + spell level (unless fall > 500 ft or spell is immediate action)
- Into water (10+ ft deep): first 20 ft no damage; next 20 ft 1d3 nonlethal per 10 ft; beyond that 1d6 lethal per 10 ft. Deliberate dive (DC 15 Swim or Acrobatics) takes no damage if water is 10 ft deep per 30 ft fallen; DC +5 per 50 ft of dive.
Falling Objects
| Object Size | Damage (base) |
|---|---|
| Small | 2d6 |
| Medium | 3d6 |
| Large | 4d6 |
| Huge | 6d6 |
| Gargantuan | 8d6 |
| Colossal | 10d6 |
| Half damage if fallen < 30 ft; double if > 150 ft. Light material (wood) may deal half. DC 15 Reflex for half if aware. Object takes same damage as it deals. | |
Heat Dangers
| Temperature | Check | Frequency | Failure |
|---|---|---|---|
| Very hot (above 90 °F) | Fort DC 15 (+1/prev); –4 in heavy armor | 1/hour | 1d4 nonlethal; unconscious = 1d4 lethal/hour |
| Severe heat (above 110 °F) | Fort DC 15 (+1/prev); –4 in heavy armor | 1/10 min | 1d4 nonlethal; unconscious = 1d4 lethal/10 min |
| Extreme heat (above 140 °F / fire / lava) | Fort DC 15 (+1/prev) for nonlethal | 1/5 min | 1d6 fire/min (no save) + 1d4 nonlethal on failed save |
Any nonlethal damage from heat causes heatstroke (fatigued). Boiling water: 1d6 scalding, or 10d6/round fully immersed.
Smoke Effects
Heavy smoke: Fort DC 15 (+1/prev) each round or spend the round choking and coughing. Two consecutive rounds of choking: 1d6 nonlethal damage. Smoke grants concealment (20% miss chance) to all creatures within it.
Starvation & Thirst
Needs (Medium): 1 gallon of fluids and ~1 lb of food per day (half for Small; 2–3× water in extreme heat).
- Water: Can go without for 1 day + Con score in hours. After: Con check DC 10 (+1/prev check) each hour or 1d6 nonlethal.
- Food: Can go without for 3 days. After: Con check DC 10 (+1/prev check) each day or 1d6 nonlethal.
- Nonlethal from thirst/starvation makes character fatigued. Cannot be healed magically — only food/water resolves it.
- When nonlethal ≥ max HP, further damage is lethal.
Suffocation
Water Dangers
- Calm water: Swim DC 10; take 10 is allowed for trained swimmers
- Fast-moving water: DC 15 Swim or Strength check or go under; 1d3 nonlethal/round (1d6 lethal over rocks)
- Deep water: 1d6 pressure damage per minute per 100 ft below surface (Fort DC 15 +1/prev negates); very cold = 1d6 nonlethal/min hypothermia
- Drowning: Hold breath for 2 × Con score rounds; after that Con check DC 10 (+1/round). Fail: round 1 unconscious (0 hp), round 2 drop to −1 and dying, round 3 drown.
Creatures can drown in substances other than water — sand, quicksand, fine dust, grain silos.
Wilderness Terrain
Getting Lost
Characters can become lost when visibility drops below 60 ft (fog, snow, darkness) or when moving cross-country through forest, moor, hill, or mountain terrain without a trail. The party leader makes a Survival check each hour or portion of an hour of local/overland movement.
| Terrain | Survival DC |
|---|---|
| Desert or plains | 14 |
| Forest | 16 |
| Moor or hill | 10 |
| Mountain | 12 |
| Open sea | 18 |
| Urban, ruins, or dungeon | 8 |
| Modifiers: +4 with proper nav tools (map, sextant); −4 poor visibility; +2 with 5+ ranks in Knowledge (geography or local). | |
Lost parties move in a random direction each hour. Once lost, a DC 20 Survival check (−1 per hour of random travel) lets a character recognize they're lost. Setting a new course requires Survival DC 15 (+2 per hour of random travel); failure gives a random "correct" direction.
Forest Terrain
| Element | Sparse | Medium | Dense |
|---|---|---|---|
| Typical trees | 50% | 70% | 80% |
| Massive trees | — | 10% | 20% |
| Light undergrowth | 50% | 70% | 50% |
| Heavy undergrowth | — | 20% | 50% |
Typical trees grant partial cover (+2 AC, +1 Reflex) to creatures in the same square. Climb DC 15. Trunk: AC 4, hardness 5, 150 hp.
Massive trees occupy a full square; full cover to adjacent creatures. AC 3, hardness 5, 600 hp.
Light undergrowth: 2 sq movement to enter; concealment; Acrobatics/Stealth DC +2.
Heavy undergrowth: 4 sq movement; 30% miss chance concealment; Acrobatics DC +5; Stealth +5 bonus; no running or charging.
Detection in forest: Sparse 3d6×10 ft; Medium 2d8×10 ft; Dense 2d6×10 ft. Sound Perception DC increases by 2 per 10 ft (not 1).
Marsh Terrain
| Element | Moor | Swamp |
|---|---|---|
| Shallow bog | 20% | 40% |
| Deep bog | 5% | 20% |
| Light undergrowth | 30% | 20% |
| Heavy undergrowth | 10% | 20% |
Shallow bog: ~1 ft deep mud/water. 2 sq movement to enter; Acrobatics DC +2.
Deep bog: ~4 ft standing water. 4 sq movement (Medium+) or swim. Small creatures must swim. Cover for Medium+ creatures; improved cover for smaller. Tumbling impossible.
Bogs increase Stealth DC by 2. Detection in moor: 6d6×10 ft; swamp: 2d8×10 ft.
Hills Terrain
| Element | Gentle Hills | Rugged Hills |
|---|---|---|
| Gradual slope | 75% | 40% |
| Steep slope | 20% | 50% |
| Cliff | 5% | 10% |
| Light undergrowth | 15% | 15% |
Gradual slope: No movement penalty; +1 melee bonus against downhill foes.
Steep slope: 2 sq movement to enter going uphill. Running/charging downhill: DC 10 Acrobatics (or Ride for mounts) or stumble (end 1d2×5 ft later; fail by 5+ = prone). Acrobatics DC +2.
Cliff: Climb DC 15; 1d4×10 ft tall. Detection: gentle 2d10×10 ft; rugged 2d6×10 ft.
Mountain Terrain
| Element | Alpine Meadow | Rugged | Forbidding |
|---|---|---|---|
| Gradual slope | 50% | 25% | 15% |
| Steep slope | 40% | 55% | 55% |
| Cliff | 10% | 15% | 20% |
| Chasm | — | 5% | 10% |
| Light undergrowth | 20% | 10% | — |
| Scree | — | 20% | 30% |
| Dense rubble | — | 20% | 30% |
Cliff: 2d6×10 ft tall in mountains (vs 1d4×10 ft in hills); Climb DC 15.
Chasm: 2d4×10 ft deep (rugged) or 2d8×10 ft (forbidding); at least 20 ft long, 5–20 ft wide; Climb DC 15 to exit.
Scree: No speed penalty but Acrobatics DC +2 (gradual slope) or +5 (steep); Stealth DC +2 on any slope.
Dense rubble: 2 sq movement; Acrobatics DC +5; Stealth DC +2.
Rock wall: DC 25 Climb; 2d4×10 ft (rugged) or 2d8×10 ft (forbidding). Detection: up to 4d10×10 ft (sound carries farther — DC increases 1 per 20 ft, not per 10 ft).
Altitude Zones
| Zone | Altitude | Effect |
|---|---|---|
| Low pass | <5,000 ft | No altitude effects |
| Low peak / high pass | 5,000–15,000 ft | Non-acclimated: Fort DC 15 (+1/prev) each hour or fatigued (until descent) |
| High peak | >15,000 ft | Altitude sickness: Fort DC 15 (+1/prev) each 6 hours or 1 damage to ALL ability scores (even acclimated, who gain +4 to saves) |
Desert Terrain
| Element | Tundra | Rocky | Sandy |
|---|---|---|---|
| Light undergrowth | 15% | 5% | 5% |
| Ice sheet | 25% | — | — |
| Light rubble | 5% | 30% | 10% |
| Dense rubble | — | 30% | 5% |
| Sand dunes | — | — | 50% |
Ice sheet: 2 sq movement; Acrobatics DC +5; DC 10 Acrobatics to run/charge.
Sand dunes: Function as hills; drift slowly with the prevailing wind.
Detection: 6d6×20 ft in open desert; 6d6×10 ft in dunes (heat distortion limits vision at longer ranges).
Plains Terrain
| Element | Farm | Grassland | Battlefield |
|---|---|---|---|
| Light undergrowth | 40% | 20% | 10% |
| Heavy undergrowth | — | 10% | — |
| Light rubble | — | — | 10% |
| Trench | 5% | — | 5% |
| Berm | — | — | 5% |
Trench: Functions as low wall except no cover vs adjacent foes; 2 sq to leave. Attacker outside gains +1 melee (higher ground).
Berm: Two rows of steep slope back-to-back; +1 sq to cross. 2-sq berm provides low-wall cover.
Fences: Wooden = +1 sq movement; stone = low-wall cover. Mounted DC 15 Ride to cross without slowing.
Detection: 6d6×40 ft (best in game).
Aquatic Terrain
Calm water: Swim DC 10. Rough: DC 15. Stormy: DC 20.
Fast rivers (60+ ft/round): DC 20 Swim each round or go under; 3 successes in a row to reach bank. Rapids = stormy (DC 20).
Vision: Clear water 4d8×10 ft; murky 1d8×10 ft. Invisible creatures displace water (20% miss, not 50%).
Spring floods: River rises 1d10+10 ft, widens ×(1d4×50%); Swim checks one category harder; 50% swifter.
Spellcasting underwater: Non-water-breathers: concentration DC 15 + spell level (in addition to any fire-spell caster-level check).
Underwater Combat
| Condition | Slash/Bludgeon | Piercing | Movement | Off-balance? |
|---|---|---|---|---|
| Freedom of movement | normal / normal | normal / normal | normal | No |
| Has swim speed | –2 / half | normal | normal | No |
| Successful Swim check | –2 / half | normal | ¼ (move) or ½ (full) | No |
| Firm footing | –2 / half | normal | half | No |
| None of the above | –2 / half | –2 / half | normal | Yes |
| Off-balance: lose Dex bonus to AC; opponents gain +2 on attacks. Fire spells need caster-level check DC 20 + spell level; nonmagical fire fails entirely. Thrown weapons useless; other ranged –2 per 5 ft of water. | ||||
Dungeon Features
Walls
| Wall Type | Thickness | Break DC | Hardness | HP (per 10×10) | Climb DC |
|---|---|---|---|---|---|
| Masonry | 1 ft | 35 | 8 | 90 | 20 |
| Superior masonry | 1 ft | 35 | 8 | 90 | 25 |
| Reinforced masonry | 1 ft | 45 | 8 | 180 | 20 |
| Hewn stone | 3 ft | 50 | 8 | 540 | 25 |
| Unworked stone | 5 ft | 65 | 8 | 900 | 15 |
| Iron | 3 in | 30 | 10 | 90 | 25 |
| Wooden | 6 in | 20 | 5 | 60 | 21 |
| Paper | Paper-thin | 1 | — | 1 | 30 |
| Magically treated | — | +20 | ×2 | ×2 (min +50 hp) | — |
Floors
- Flagstone: Most common; no penalty when intact.
- Uneven flagstone / hewn stone: DC 10 Acrobatics to run or charge.
- Light rubble: Acrobatics DC +2.
- Dense rubble: 2 sq movement; Acrobatics DC +5; Stealth DC +2.
- Natural stone: 2 sq movement; Acrobatics DC +5; no running/charging except on paths.
- Slippery (water, ice, blood, slime): Acrobatics DC +5 to any floor type.
- Grate: Iron grate 1 in thick — AC 2, hardness 10, 25 hp, break DC 27.
- Ledge: ≤12 in wide requires Acrobatics check to move; railing grants +5 to that check.
Doors
| Door Type | Thickness | Hardness | HP | Break DC (Stuck) | Break DC (Locked) |
|---|---|---|---|---|---|
| Simple wooden | 1 in | 5 | 10 | 13 | 15 |
| Good wooden | 1½ in | 5 | 15 | 16 | 18 |
| Strong wooden | 2 in | 5 | 20 | 23 | 25 |
| Stone | 4 in | 8 | 60 | 28 | 28 |
| Iron | 2 in | 10 | 60 | 28 | 28 |
| Portcullis, wooden | 3 in | 5 | 30 | 25* (lift DC) | |
| Portcullis, iron | 2 in | 10 | 60 | 25* (lift DC) | |
| Lock | — | 15 | 30 | Disable Device DC 20–30 | |
| ~10% of wooden doors and 5% of non-wooden doors are stuck (double in neglected dungeons). Wooden bar: DC 25 to break through; iron bar: DC 30. | |||||
Cave-Ins and Collapses CR 8
A weakened ceiling can be spotted with DC 20 Knowledge (engineering) or Craft (stonemasonry). Destroying half the pillars supporting a ceiling can cause a collapse.
- Bury zone: 8d6 damage (DC 15 Reflex for half); buried on any result.
- Slide zone: 3d6 damage (DC 15 Reflex negates); buried on fail.
- While buried: 1d6 nonlethal/min; unconscious → DC 15 Con or 1d6 lethal/min.
- Digging out: 1 minute clears rocks equal to 5× heavy load; armed digger clears twice as fast. DC 25 Strength to self-extract.
Slimes, Molds & Fungi
Weather
Random Weather
| d% | Result | Cold Climate | Temperate | Desert |
|---|---|---|---|---|
| 01–70 | Normal | Cold, calm | Normal for season | Hot, calm |
| 71–80 | Abnormal | Heat wave (01–30) or cold snap (31–100) | Heat wave (01–50) or cold snap (51–100) | Hot, windy |
| 81–90 | Inclement | Snow | Precipitation (season) | Hot, windy |
| 91–99 | Storm | Snowstorm | Thunderstorm / snowstorm | Duststorm |
| 100 | Powerful storm | Blizzard | Windstorm / blizzard / hurricane / tornado | Downpour |
| Temperate includes forests, hills, marshes, mountains, plains, and warm aquatic. Cold snap −10 °F; heat wave +10 °F. | ||||
Precipitation
Roll d% for type: 01–30 fog · 31–90 rain/snow · 91–00 sleet/hail. Snow/sleet only at ≤30 °F. Most precipitation lasts 2d4 hours; hail lasts 1d20 minutes.
- Rain: Visibility ½; –4 Perception; same as severe wind on flames and ranged attacks.
- Snow: Same as rain; 2 sq movement per snow-covered square; 1d6 inches deposited.
- Heavy snow: Fog-like visibility; 4 sq movement; 1d4 ft deposited; 10% chance of lightning.
- Sleet: Same as rain while falling; same as snow on ground.
- Hail: No visibility reduction; –4 sound Perception; 5% chance 1 lethal damage per storm in the open.
- Fog: Blocks all sight beyond 5 ft (including darkvision); 20% miss chance against creatures 5 ft away.
- Downpour: Treats as rain but conceals as fog; can create floods; lasts 2d4 hours.
Storms
Storms reduce visibility by ¾ (–8 Perception). Ranged attacks impossible; siege weapons –4. Automatically extinguish unprotected flames; 50% chance to extinguish protected flames. Last 2d4–1 hours.
Wind Effects
| Wind Force | Speed | Ranged (Normal/Siege) | Checked Size | Blown Away Size | Fly Penalty |
|---|---|---|---|---|---|
| Light | 0–10 mph | —/— | — | — | — |
| Moderate | 11–20 mph | —/— | — | — | — |
| Strong | 21–30 mph | –2/— | Tiny | — | –2 |
| Severe | 31–50 mph | –4/— | Small | Tiny | –4 |
| Windstorm | 51–74 mph | Impossible/–4 | Medium | Small | –8 |
| Hurricane | 75–174 mph | Impossible/–8 | Large | Medium | –12 |
| Tornado CR 10 | 175–300 mph | Impossible/impossible | Huge | Large | –16 |
| Checked: DC 10 Strength (ground) or DC 20 Fly to move forward. Blown away (ground): knocked prone + rolled 1d4×10 ft (1d4 nonlethal per 10 ft) unless DC 15 Strength. Blown away (flying): 2d6×10 ft back + 2d6 nonlethal unless DC 25 Fly. Tornado funnel contact: 1d10 rounds inside, 6d6/round, then flung (fall damage may apply). | |||||
Urban Adventures
City Walls & Gates
| City Size | Thickness | Height | Climb DC | HP (per 10-ft section) |
|---|---|---|---|---|
| Small city | 5 ft | 20 ft | 30 | 450 (AC 3, hardness 8) |
| Large city | 10 ft | 30 ft | 30 | 720 (AC 3, hardness 8) |
| Metropolis | 15 ft | 40 ft | 30 | 1,170 (AC 3, hardness 8) |
| Gates: typically two portcullises with murder holes between. Gates open during day; locked/barred at night. Watchtowers 10 ft taller than adjoining wall. | ||||
Guards & Soldiers
- City guard (full-time): 1% of adult population; 80% on patrol, 20% posted.
- Militia (conscript): 5% of population; called up only during attack.
- Shifts: Day 30% · Evening 35% · Night 35%. One guard post per neighborhood.
- Majority are 1st-level warriors; officers include higher warriors, fighters, clerics, and arcane casters.
Siege Engines
| Engine | Cost | Damage | Critical | Range Increment | Crew |
|---|---|---|---|---|---|
| Catapult, heavy | 800 gp | 6d6 | — | 200 ft (100 ft min) | 4 |
| Catapult, light | 550 gp | 4d6 | — | 150 ft (100 ft min) | 2 |
| Ballista | 500 gp | 3d8 | 19–20 | 120 ft | 1 |
| Ram | 1,000 gp | 3d6* | — | — | 10 |
| Siege tower | 2,000 gp | — | — | — | 20 |
| * Ram: up to 9 additional crew add Strength modifier to damage. Catapult uses special attack checks (base attack + Int + range penalty) vs DC 15. Misfire: 1d8 direction, 1d4 range increments off. Siege engine stats: AC 3, hardness 5, 80 hp. | |||||
City Streets & Features
Typical streets 15–20 ft wide; alleys 5–10 ft. Main roads 25 ft + 5-ft sidewalks. Cobblestones in poor repair or rutted dirt = light rubble (Acrobatics DC +2).
Crowds: 2 sq movement to enter; provide cover. Move away at 30 ft/round (init 0) if danger is obvious. Diplomacy DC 15 or Intimidate DC 20 to direct a crowd.
Lower-story walls: 1 ft thick, AC 3, hardness 8, 90 hp, Climb DC 25. Upper stories: 6 in, hardness 5, 60 hp, Climb DC 21.
Rooftops: flat = normal movement; pitched peak DC 20 Acrobatics; slope parallel to peak DC 15; crossing peak DC 10.
Sewers: open grate (full-round), drop 10 ft. Built like dungeons — slippery floors common.
GMG Sample Hazards
Hazards are location-based threats with CRs like traps or monsters — environmental, living, or magical. Each has a trigger condition, a means of detection, and a way to eliminate it.
Non-flammable gas (CR 1): DC 25 Survival to notice (invisible). Fort DC 15 (+1/prev) each hour or fatigued; after fatigued, slow suffocation begins.
Flammable gas (CR 4): Same fatigue; plus open flame/spark causes explosion — 6d6 fire (DC 15 Reflex for half) to all in cavern or within 5 ft of entrance. Air unbreathable for 2d4 minutes after explosion.
Infestation: Fort DC 15; frequency 1/hour; effect 1d6 Con damage; onset 4d6 hours. No save ends it — only remove disease.
CR 1 (contact): Fort DC 13; onset 1 hour; 1d4 Dex + sickened until damage healed; 1 save to cure.
CR 3 (severe — full body or smoke inhalation): Fort DC 16; onset 1 hour; initial 2d4 Dex + 1d4 Con + sickened; secondary 1 Con/hour; 1 save to cure. (Smoke from stinging nettles is not hazardous.)
Once infested, burrow toward heart/brain. Round 1: flame at wound kills them (1d6 fire to victim). Cut out with DC 20 Heal (slashing) — 1d6 damage per round host has been infested; removes 1 grub. Remove disease kills all grubs.
Infestation: Fort DC 17; frequency 1/round; effect 1d2 Con per grub; onset immediate.
Disasters
Disasters are adventure-scale events without a single CR — treat each phase as a separate encounter sized appropriately for the party. Adjust pacing from minutes to days as needed.
Volcanoes
Tsunamis
Caused by underwater earthquakes, volcanic explosions, landslides, or asteroid impacts. Nearly undetectable until reaching shallow water. Wave travels hundreds of yards to a mile inland.
- Structures: Obliterates or displaces all temporary/poor buildings; destroys ~25% of well-built buildings; leaves serious fortifications lightly damaged.
- Population: ~25% of population killed (swept out to sea, drowned, or buried in rubble).
- Swept away: DC 25 Swim or pulled 6d6×10 ft away from shore.
- Post-tsunami water: Always rough or stormy barring magical calming.
- Collapsing building: 6d6 damage (DC 15 Reflex for half); 50% chance of being buried (as cave-in).
Undead Uprising
An undead uprising unfolds in waves over days or weeks. During daylight hours life returns to some normalcy as sunlight briefly suppresses the undead's power.