GM Advice: What Lies Under the Streets

Adventures set under a city’s streets invariable feature networks of dank, noisome sewers. There are other locations, however, a GM could consider as the setting for his adventure.

By William McAusland (Outland Arts)
By William McAusland (Outland Arts)


A city’s underworld should be a dynamic, complex place. Such locations can be immense and comprise a vast range of different types of locale. Much more lies beneath the streets than mere sewers. The following places could be found below a city:

  • Rivers & Canals: Sometimes rivers and canals get diverted underground to make way for buildings and thoroughfares. Such underground waterways often interlink with the settlement’s sewers.
  • Crypts: The city must bury its dead and with space above ground at a premium often the dead get interred underground. Crypts can be found below practically every church, chapel and shrine in the city. Some wealthy families might maintain private crypts beneath their urban estates. Space in crypts are normally reserved for the great and the good. For everyone else, the anonymity of the catacombs awaits…
  • Catacombs: In these vast burial complexes are laid to rest the great unwashed of the city. Some such places may be organised. Families and neighbourhoods might have their own portions of the catacombs in the same way as they would have a cemetery above ground. In others, the dead are simply placed wherever is expedient.
  • Reservoirs: Towns and cities have a terrible thirst. The populace and industry of the place require water – and lots of it. Reservoirs or cisterns are built to provide a place to store water against times of need. Such locations are particularly common in settlements without ready access to a nearby source of fresh water.
  • Vaults: Every town has a wealthy upper class and every upper class family has treasure they wish to keep safe. Some vaults will be private while others are communal affairs or are run as businesses. Such locations are always heavily guarded, but are attractive targets for thieves due to the concentration of wealth in one place.
  • Quarries: Building a town or city often requires stone (at least for the major buildings). It is costly and time consuming to transport such stone long distances. Sometimes, the settlement expands to surround or grow over a quarry. This can be dangerous. If the ground below buildings is unstable sink-holes or collapses can occur.
  • Mines: In the same way as quarries, mines can tunnel under a town for great distances.
  • Homes: In some settlements, a significant portion of the populace may live underground. Some races such as dwarves love living underground while other individuals – the very poor, the desperate and the hunted – might be forced underground. Whole communities and neighbours might exist under the city streets.

Remember underground locales can be adapted and changed to suit the user’s needs. A played out underground mine or quarry could be transformed into a mushroom farm, for example. While an underground reservoir could also be used to farm fish.

Help Fellow GMs!

Have you used other underground spaces in urban adventures? Let us know what they are in the comments below and help fellow GMs build better urban adventures today!

This post is part of Urban Week. Urban Week celebrates the release of GM’s Miscellany: Urban Dressing from Raging Swan Press which is available from Thursday 26 June. I hope you find it useful and that it enhances your urban campaigns!

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Creighton is the publisher at Raging Swan Press and the designer of the award winning adventure Madness at Gardmore Abbey. He has designed many critically acclaimed modules such as Retribution and Shadowed Keep on the Borderlands and worked with Wizards of the Coast, Paizo, Expeditious Retreat Press, Rite Publishing and Kobold Press.

5 thoughts on “GM Advice: What Lies Under the Streets”

  1. I ran an adventure where the middens under each house in a town were connected and ruled by a were-rat that also doubled as the town’s garbage handler. He was allowed to live so long as he did not breed (so to speak) and kept the underground clean and free of issues. The party stumbled upon the midden tunnels by accident and killed the rat man as they thought they were helping the town out but alas they were put on trial for the murder and forced to find another creature such as previous to do the job. It was an interesting time to say the least.

  2. Very often, beneath very old cities lie the bones of ancient civilizations. These ruins beneath the city can easily be the hideout of a thieves’ guild, or the court of the local vampire clan. The ruins can be as elaborate as needed. A thieve’s guild will make use of the ruins as they are, while a vampire noble might very well renovate the structures and bring them back to a level of elegance. Ruins could be built upon ruins, creating a labyrinth of ancient cities. Dwarves could have moved into the ancient underground city and rebuilt it. They may have need of adventurers to defend their city from the creepy crawlies that lie beneath them.

  3. Urban adventures need to have an underground part. If you ever tried to map a town, you always are confronted with the sewer system, and all illegal activities run by thieves guilds, smugglers and Evil cults.
    Don’t forget Evil cults : their places of worship are often underground, and the secrecy needed for the vile activities of its members are more easy to maintain when you don’t have to move in plain sight. You can have organized lawful groups like Devil worshipers with buried cathedral, bestial and chaotic congregation with cavern-like temple, eventually connected with under-Oerth races by deep tunnels.
    The reverse can also be true : in evil kingdoms, good cults may eventually try to regroup their worshipers in underground place, as first Christians used to do in Rome.
    More ancient cities can have long lost magic running underneath. Forgotten crypts with artefacts that produce strange effects, odd golems waiting for centuries suddenly animates , automatic systems to produce water for places without natural waterways begin to go awry and unleash elemental creatures in the sewers, automatic summon systems bring in creatures (e.g. gelatinous cubes) to clean underground passageways…
    For the best results with underground city adventure, I suggest to use several groups that compete for this territory. Try to build balance between these factions (thieves, beggars, slavers, cultists, fugitives, strange monsters, minded undeads, wererats …) with many alliances between them and people in the surface town (officials, nobles, sages, traders, alchemist and wizards…). Throw the player in with some minor problem that force them to go under the streets and let’s the fun begin…
    Just my 2 cents.
    Alain a.k.a the MadJester.

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