The Forgotten Vault Below the Sewer

The Forgotten Vault is a dungeon for fantasy roleplaying games set in the sewers below a city. The dungeon is setting and system neutral for easy adaptation and improvisation. This post is not a full adventure, but rather an adventure framework with three maps. You can change, swap, and expanded any part as you desire.

Adventure Background

The Forgotten Vault was once part of a palace in the city, or a larger underground complex of a powerful cult or mage guild, but is now a crumbling ruin below the city sewers and catacombs. The complex is now buried and forgotten, and only parts like the sanctum are now accessible through new secret tunnels from the city above. The past now exists in fading memory and vague text fragments.

The following backgrounds may be appropriate for your game.

Tyrant’s Palace. A tyrant of centuries past resided in a grand palace in the city. The tyrant eventually passed, the palace fell to ruin, and was demolished to make room for new buildings. Time passed, the city grew and changed, and both the tyrant and the palace were forgotten.

The Fallen Mage Guild. A mage guild once resided in the city and used a well-defended palace as headquarters. The guild eventually fell out of favor or needed a larger facility, and sold the old the guild house. A few of the dungeon levels were simply sealed off until someone found a new use for them. This never occurred, and the sublevel was forgotten.

The Templar’s Sacristy. Religious wars, hidden or otherwise, have raged as long as anyone can remember. The Templar Order built fortresses and strongholds to the front over the past centuries. The church’s enemies have destroyed some while others have become redundant with the shifting frontlines. Other strongholds have always been secret and were eventually lost as the Templar Order lost vital members.

Adventure Hooks

Choose any of the following adventure hooks, or make one of your own.

The Dead Archeologist. It is a time of religious strife, and lost secrets from the past gain new relevance. Occultists and Divine Seekers travel far and wide as they look into all sorts of ruins and haunted places. A maid at a local inn found one such individual dead this morning in bed after spending the night investigating a tavern cellar.

The Lost Royal Blade. Civil war is brewing, and the would-be contenders look desperately for any ties to past royalty. Some folks claim a lost blade belonging to the royal house was brought to the city in a previous conflict. A conspiracy hid the sword in a hidden vault but was forgotten when the conspirators were killed by assassins. Recently recovered documents from foreign occultists show the approximate area in the city. Anyone searching the city sewers and basements in the area should have a chance of finding a more precise location.

Doomsayer’s Secrets. A doomsayer has haunted a city corner for months spewing dark prophecies of rising demons and threats to the wealthy townsfolk. It was probably just a matter of time before someone put him out of his misery, and no one was surprised when he went missing. The city watch found him a week later, clawing the wall in the sewer muttering “the church must be told” repeatedly. Someone killed the doomsayer in prison a few days later, and the murder remains unsolved.

The Dank Sewers

Old cities have layers. The sewers are just below the city, often half-collapsed spiderwebs of pipes, tunnels, and chambers. There are also some chambers are better forgotten.

Anything build below the sewers is likely to be damp and rotting, covered with layers of sediments and sewage traces. The dungeon residents are likely to be rodents, constructs, undead, and things better forgotten. Thieves, cultists, and smugglers use the sewer to hide their activities.

However, the dungeon may be suitable for hiding items of interest and carefully sealed supplies.

The Forgotten Vault is a dungeon located below the sewer of a fantasy city. The dungeon is setting and system neutral, and are easily adaptable.
Old cities have layers. Just below the city are the sewers, often half-collapsed spiderwebs of pipes, tunnels, and chambers. Some chambers are better forgotten.

The Lost Sewer Entrance

The entrance to the Forgotten Vault is long gone, sealed by an alliance of elves and air elementals, and collapsed under the weight of the growing city above. Cultists have tunneled a new entrance and hid it behind a secret door from the sewers.

The Forgotten Vault is a dungeon located below the sewer of a fantasy city. The dungeon is setting and system neutral, and are easily adaptable.
The actual entrance to the Forgotten Vault is long gone, sealed by an alliance of elves and air elementals, sealed and collapsed under the weight of the growing city above. Cultists eventually tunneled a new entrance and hid it behind a secret door from the sewers.

The Secret Entrance. Behind the secret door in the sewer is a short passage of the uncut stone. The passage is wet and slimy of water overflow and sewage and leads to the stairs down to the Upper Foyer.

Elven runes are etched into the tunnel wall. “Beware, the fire bringer lingers,” is barely readable, and the rest is unreadable.

The Upper Foyer. The room was once the middle chamber of a grand stair. The stairs up on the east wall are collapsed, while the stairs on the south wall are usable.

A crumbling statue of an imposing bearded man dressed in mage robes wearing a tall cone-shaped hat is by the north wall. The man is carrying a serpentine staff and an orb.

The stairs lead down to the Fire Monks’ Hall.

The Fire Monks’ Hall. The stairs down from the Upper Foyer lead to a hall with four statues of stout fiery humanoids wearing monk robes. All four look grim and hostile.

The Forgotten Vault

The Forgotten Vault is close to the heart of the original inhabitants’ operation. The treasury, the binding chamber, the secret library – a place of secrets and wealth. The vault had passages to other sections of the original dungeon and even deeper levels, but these passages may be collapsed or lost.

The Forgotten Vault is a dungeon located below the sewer of a fantasy city. The dungeon is setting and system neutral, and are easily adaptable.
The Forgotten Vault is close to the heart of the original inhabitants’ operation. The treasury, the binding chamber, the secret library – a place of secrets and wealth. The vault had passages to other sections of the original dungeon and even deeper levels, but these passages may be collapsed or lost.

The Forgotten Vault has a foyer, three side chambers, and a hallway connected to the foyer and the ritual chamber. There are one entrance from The Fire Monks’ Hall above, a sealed passage from the Lower Foyer to other areas below the city, and a hidden stair in the southwest end of the level leading further down below the city. The exits are beyond the scope of this adventure and left to the GM to develop.

The Lower Foyer. The stairs from the Fire Monks’ Hall end in a Lower Foyer. Opposing the stairs up is a short stair down to the hallway. There are three side-chambers and a passage to another part to the dungeon from the Lower Foyer. This passage is possibly sealed and hidden at the GM’s discretion.

Four statues portraying fiery warriors, carrying halberds in one hand and with fire blazing from the other hand, line the foyer. The warriors wear half-helmets, and fangs are visible in their mouths.

The Side-Chambers. The Side-Chambers was last used by cultists. The west chamber is a sleeping chamber with bunks for the cultists. The east chamber is a cell for sacrifice prisoners.

The Hallway. The hallway connects the Lower Foyer and the Ritual Chamber. There are a statue and a short stair down at the east at the end of the hallway. The stair leads to the Ritual Chamber. The statue portrays a finely robed devilish human man who once was lord of the dungeon.

The Ritual Chamber. This large chamber was once a vital ritual chamber but was cleansed in the aftermath of the lord’s defeat. Yet, malign magic lingers here, waiting to the harnessed by evil spellcasters.

Cultists have set up a shrine in a large chamber of the vault and use the chamber for summoning devils to further their plans. The cultists deem this the safest place in the vault and use a hidden compartment in the floor for treasure and secret that may lead to adventures elsewhere.

The chamber is magically darkened, allowing only 5 feet vision with ordinary light.

The Fire Altar. There is a rust-stained altar with an eternal flame in the room. The altar is decorated with diabolic fire motifs.

The Secret Vault. The Secret Vault is accessible from both the Ritual Chamber and through a secret passage to a side chamber.

There is a statue of a robed woman wearing a full-face mask and carrying a halberd in the south end of the vault.

The secret chamber inside the Secret Vault reserved for the most valued treasures and maybe unknown to the vault’s current residents.

What Happens Next?

The adventurers may return to the inn to rest and split the loot, but find themselves on a murder scene. Maps and journals found in the Forgotten Vault may lead to caves in the Hinterlands outside the city or even a Binder’s Sanctum. A sinister warehouse or derelict crooked house in the city may be other cultist hideouts and be the launching point of counterattacks from the cult.

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