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The typical sewers beneath fantasy cities are magnificent public works from a bygone age. A mishmash of deserted concourses, covered riverways, claustrophobic tunnels, and buried ruins, they are a royal road for thieves, monsters, and adventurers alike.

Tiers. Sewers are rarely tier 3 or 4. Below the sewers, deeper and more dangerous areas are usually ruins, tombs, or other locations.

Sewer Size. Each 100-foot-square node of a sewer contains passages. Some of these passage nodes also contain a room or chamber at an intersection or dead end. A sewer typically spans the oldest or richest parts of a city and can cover as much as a square mile.

Disease. Sewers are filthy. A humanoid that takes damage while in a sewer is exposed to disease. At the end of its next long rest , the creature must succeed on a DC 11 Constitution saving throw or be infected with sewer plague.

Creating a Sewer

To generate a new map, roll on the Description table for the initial area and follow its instructions, and then do so again to see what’s past each exit, and so on. If you’re filling a pre-made map, roll on Inhabitants and Contents for each location.

Sewer: Description


1 - 5

Narrow passage. Roll on Passage Contents and Exits. For passage width, roll 1d6:

1 1 1/2 ft. pipe
2 - 3 2 1/2 ft. pipe
4 - 6 5 ft. tunnel

6 - 11

Passage. 10 feet wide. Roll on Passage Contents and Exits.

12 - 14

Wide passage. Roll on Passage Contents and Exits. For passage width, roll 1d6:

1 15 ft.
2 - 3 20 ft., 5-foot-wide walkways on either side of flowing water
4 - 6 30 ft., 10-foot-wide catwalk or gallery above flowing water
15 - 20 Chamber. Roll on Chamber Contents and Exits. For chamber size, roll 1d6:
1 20 × 20 ft.
2 30 × 30 ft.
3 - 4 40 × 40 ft.
5 40 × 50 ft.
6 50 × 50 ft.


Sewer: Passage Contents

1 - 10


11 - 14

Roll on Passage Scenery


Roll on Novelties


Roll on Obstacles

17 Roll on Discoveries
18 - 20 Roll on Escalations


Ruin: Room and Chamber Contents

Roll 1d20 in small room, 1d20 + 2 in large chamber.



2 - 5 Roll on Chamber Scenery
6 - 8

Roll on Novelties

9 - 11

Roll on Obstacles

12 - 13

Roll on Discoveries

14 - 16

Roll on Escalations and on Chamber Scenery

17 - 20

Roll on Set Pieces


Sewer: Exits

All exits are passages. Roll 1d12 on Description table for passage size.


No Exits

2 - 3

One exit left

4 - 7

One exit straight

8 - 9

One exit right


Two exits, left and right

11 - 12

Two exits, left and straight

13 - 14

Two exits, straight and right

15 - 16

Three exits, left, straight, and right

17 - 20 Ascent or descent. Roll 1d12. Then roll again on this table for other exits.
1 - 2

Slimy stone stairs down

3 - 4

Grating up


Grating down


Pipe up

7 - 8

Pipe down


Metal ladder up


Metal ladder down


Sloping waterway up or down (50 percent chance of each)


Pulley elevator up or down (50 percent chance of each)


Sewer: Novelties


A filthy altar surrounded by torches and arcane markings


Cult shrine to a prohibited faith


Amidst moldy bedrolls, a faded map of the sewers with various locations marked is pinned to the wall


Makeshift classroom. A selection of thieves’ cant glyphs and their meanings is written on the wall


Bioluminescent, telepathic mold grows on the walls. It is friendly and converses telepathically with passers-by


A pool of congealed alchemical slurry. A creature that touches the slurry regains 3 (1d6) hit points, recovers a 1st-level spell slot, and becomes poisoned for 1 hour. The slurry then becomes inert


A gigantic snakeskin fills most of the room. The scales glow with a soft, iridescent light


A disused side passage is overgrown with edible fungus


A partially collapsed tunnel conceals a clean and dry area that provides sanctuary for one long rest


Makeshift docks line the banks of an underground river or lake


Steel or stone supports are spaced evenly around the area, indicating something unusually heavy above


Water flows from a pipe high on the wall, creating an oddly beautiful waterfall


Sewer: Obstacles


Lock: The entire area is flooded with sewage, and the valve to drain it is missing a handle.

Key: A handle that fits the valve


Lock: An iron door has rusted shut (DC 18 Strength check to open).

Key: A flask of a solution that dissolves the rust, allowing the door to operate freely


Lock: Jammed sluice gate.

Key: Long bar that can pry open the gate


Lock: Iron grate secured with a padlock that has rusted solid (DC 18 Strength check to open).

Key: A set of bolt cutters that can cut through the padlock


Pocket of poisonous gas. Area is affected as per the cloudkill spell


Vast pool of raw sewage with no apparent way across


Fast-moving storm drain current with no bridge across


A dry “sluice gate” in an odd place conceals an exit


Magical illusion of a mass of waste blocking an exit. DC 13 Perception check: no smell

10 - 11

A submerged exit leads to a flooded tunnel

12 - 13

A tight squeeze through an exit tunnel, 1d12 + 12 inches wide


Draining a cistern reveals a concealed exit

15 - 20

Trap based on the dungeon level: level 1–2 acid bucket trap or slippery floor trap; 3–4 oil pool trap or poison gas trap ; 5–10 gelatinous cube pit trap or ratling-catcher trap ; 11–16 monster pit trap or water-filled room; 17–20 plague poison lock or water-filled dungeon


Sewer: Discoveries

1 - 4

Roll 1d4 on the Obstacles table. You find the key listed in that entry. Make a note of the matching lock. The next Obstacle encountered is that lock.


Supply cache. Contains 2d6 days of rations, 1d4 50-foot coils of rope, two sets of climber’s gear, a healer’s kit, a hatchet, 1d4 ladders, a pickaxe, and two daggers


Armory. Contains 1d10 nonmagical simple or martial weapons and two suits of Medium or Small leather armor


Ratling larder. Crates of food are patrolled by cats that keep tiny vermin at bay


Cultist cache. Boxes and jars filled with ritual components and 2d6 spell scrolls of level 1d4 - 1 (results of 0 indicate a cantrip) are crammed in poorly concealed shelves


Minor Treasure hidden behind a waterfall of filth


Recently hatched dragon, smaller than a wyrmling (use stats for a lizard )


The sewer connects to the cellar of a noble’s townhouse or other above-ground structure


The bottom of a wishing well; the area is strewn with 6d6 gp worth of copper and silver coins


Sewer: Escalations

50 percent of guards possess a Minor Treasure.


Guards: on patrol on behalf of the surface city or the sewer’s local overlord (roll or choose from Set Pieces). Demand to know intruders’ business

Level 1–2: 1d8 bandits or guards

Level 3–4: 1d8 soldiers ; 3 thugs

Level 5–10: veteran with 1d6 thugs

Level 11–16: 2 or 3 blackguards or gladiators

Level 17–20: assassin with 1d6 + 4 cutthroats or thugs


Guards: skulking near their secret lair

Level 1–2: 1d8 cultists

Level 3–4: 3 or 4 cutthroats or thugs

Level 5–10: 2 or 3 doppelgangers

Level 11–16: 2 cambions , night hags , or vampire spawn

Level 17–20: vampire with vampire spawn


Intruders: stealthily passing by on their way somewhere else

Level 1–2: 1 or 2 cutthroats or thugs

Level 3–4: doppelganger or oozefolk oozemancer (DDG)

Level 5–10: alchemist or assassin

Level 11–16: vampire , vampire assassin , or vampire mage

Level 17–20: master assassin , master thief , or 2 assassins


Denizens: hunting

Level 1–2: 2 or 3 ratling scavengers

Level 3–4: dire centipede , gelatinous cube , or gelatinous tube

Level 5–10: 2 or 3 euphoria jellies (DDG) or flash cubes (DDG)

Level 11–16: troll hulk (DDG)

Level 17–20: 2 assassins or ur-otyughs


Denizens: in lair

Level 1–2: 2d4 giant rats or poisonous snakes

Level 3–4: 3 ghouls or shadows

Level 5–10: otyugh , ur-otyugh , or sewer chimera

Level 11–16: 2 elder black puddings or otyughs

Level 17–20: rakshasa with cambion

6 - 8

Roll 1d6 on this table to determine an encounter group. The group is nearby (in the nearest unexplored room) and may be detected by tracks, noises, flickering torchlight, or other signs


Sewer: Set Pieces

Set piece encounters usually feature a Treasure Hoard.

1 - 2

Criminal Hideout. A gang or thieves’ guild has a base here.

Level 1–2: 1 or 2 thugs with 1d4 bandits or wolves

Level 3–4: crime boss or gladiator with 1 or 2 thugs

Level 5–10: assassin with 1 or 2 veterans

Level 11–16: archmage or master assassin with 2 assassins

Level 17–20: master assassin or 3 gladiators with 3 assassins and 1 mage

Setting: The area resembles an underground shantytown with numerous tight passages and close corners. Visibility is limited to a range of 20 feet before a corner or makeshift structure blocks line of sight.

3 - 4

Sewer Predator. Something hungry and dangerous lurks under the water.

Level 1–2: 2 giant constrictor snakes , gibbering mouthers , or will-o’-wisps

Level 3–4: giant crocodile and 1d4 + 1 crocodiles ; sewer chimera

Level 5–10: ur-otyugh and 1 or 2 otyughs ; hydra

Level 11–16: troll hulk (DDG) and 2 or 3 trolls

Level 17–20: draconic horror (DDG) and 2 or 3 murmuring worms or behirs

Setting: The creature’s watery lair is full of unpredictable currents. On initiative count 20 each round, a wave sweeps through the area in a random direction. Creatures that fail a Strength saving throw (DC 10 + half dungeon level) are pushed 30 feet in the direction of the flow. The predators can choose to fail or automatically succeed on this saving throw.

5 - 6

Cult Cell. Cultists hide their illicit activities below cities for many of the same reasons ordinary criminals do, and the reach of the sewer tunnels means they can snatch victims from anywhere.

Level 1–2: cult fanatic with 1d4 cultists

Level 3–4: 1 or 2 cult fanatics with 2 oculites (DDG)

Level 5–10: forgotten god or glabrezu with 1d4 cult fanatics

Level 11–16: aboleth , aboleth champion (DDG), and 1d6 maw swarms (DDG)

Level 17–20: aboleth fallen ascendant (DDG), aboleth , and 2 or 3 aboleth champions (DDG)

Setting: The area features an altar and a central pool filled with black water that obscures the vision of trespassers only. Creatures with a swim speed gain total concealment while beneath the water. Cultists attempt to herd interlopers near the water.

7 - 8

Tide-driven stone gates close behind the adventurers, forcing them to escape via a 100-foot underwater swim through fetid water. At the start of each of its turns, each creature in the water must succeed on a Constitution saving throw (DC 10 + half dungeon level) or become poisoned and unable to hold its breath. At the end of the swim, a metal grate (DC 10 + half dungeon level Strength check to break) blocks the exit.

9 - 10

A sluice gate opens, creating a waterfall that sweeps the adventurers to a new area or out of the sewer. Each creature must make three Strength, Dexterity, or Constitution saving throws (their choice), taking 2 (1d4) damage per dungeon level per failure.


Sewer: Minor Treasure



Set of directions that leads to treasure — possibly in a mansion accessible through the sewer


Spell scroll containing a spell appropriate to the area’s tier (tier 0: cantrip or level 1 spell, tier 1: level 2–3 spell, tier 2: level 4–5 spell, tier 3: level 6–7, tier 4: level 8–9)

3 - 6

Treasure worth an amount appropriate to the tier (tier 0: 10 gp, tier 1: 100 gp, tier 2: 1,000 gp, tier 3: 10,000 gp, tier 4: 100,000 gp). Roll
1d10 to determine treasure type: 1–3 coins, 4–6 jewelry, 7–8 obviously stolen housewares, 9 fiendish idol, 10 forbidden tome


1d6 vials. Roll 1d6: 1–3 potions of healing , 5–6 potions of water breathing

8 - 10 Ring, necklace, or other jewelry, worth an amount appropriate to the tier (tier 0: 25 gp, tier 1: 75 gp, tier 2: 750 gp, tier 3: 2,500 gp, tier 4: 25,000 gp)


Sewer: Treasure Hoards

Dungeon Level 1–2

Valuables: 1d4 × 100 gp in copper, silver, or gold coins

Magic (30 percent chance): pipes of the sewers or ring of swimming

Dungeon Level 3–4

Valuables: 2d4 × 100 gp in gold coins or jewelry

Magic (40 percent chance): cloak of protection or ring of water walking

Dungeon Level 5–10

Valuables: 1d6 × 1,000 gp in gold coins, bulky housewares, or jewelry

Magic (50 percent chance): dagger of venom or ring of evasion

Dungeon Level 11–16

Valuables: 1d4 × 10,000 gp in gold and platinum coins or gems

Magic (60 percent chance): folding boat or nine lives stealer

Dungeon Level 17–20

Valuables: 1d4 × 100,000 gp in gold coins, gems, or property deeds

Magic (70 percent chance): luck blade or well of many worlds


Sewer: Passage Scenery

1 - 4

Footbridges across drainage channel in middle of passage

5 - 7

Filthy, stinking mud makes the area difficult terrain

8 - 9

Mundane graffiti or thieves’ cant glyphs on walls. May contain useful information

10 - 11

Drainage channel covered with boards. There’s a table and chairs and a couple of bookcases full of moldy books


An open secret door reveals empty barrels and crates


Predator’s den containing gnawed bones and other garbage


Cement or stone blocks attached to chains, used by a local criminal element to dispose bodies


Sewer grate leads to a secret above-ground hideout


Ossuary. Neat stacks of humanoid bones fill niches. Memorial plaques identify the remains


Outflow tunnel. Water streams through a heavy grate into a nearby body of water, such as a river or lake


Benches and tools fill a makeshift workspace. The usual board flooring is reinforced with heavier beams and metal braces.


Abandoned, one-person hovel containing candles and a sleeping pallet


A stack of 10-foot poles affixed with hooks, used for dredging drainage channels


Sewer: Chamber Scenery


1 - 3

Storm runoff reservoir. The water is relatively clean and clear

4 - 7

Reservoir full of raw sewage

8 - 9

Flow control room. A vast array of pipes and valves

10 - 11

Fast-moving water with several sturdy access bridges across the flow


Maintenance storage area. Spare lengths of pipe are stacked neatly on pallets. Tools hang on peg boards behind locked grates


Barrels of lye and other chemicals (treat as acid) are covered in tarps


The exits are hatches like those found on a submarine


Eggs incubating in a nest of warm filth; depending on the tier, the eggs may hatch into giant centipedes , crocodiles , dinosaurs, or otyughs

16 - 17

One exit leads to ancient ruins. Switch to the ruin tables for the areas in this direction

18 - 19

One exit leads to catacombs. Switch to the tomb tables for the areas in this direction


One exit leads to natural caves. Switch to the Freelinking: Node title cavern does not exist tables for the areas in this direction