The Sunken Vault
A thieves' guild stripped a prestigious underground bank hours before the river broke through its old foundations. The result is a half-drowned vault full of desperate looters, trapped wealth, and one last chamber the guild could not crack before the water rose.
Get a Fresh Drop Every Week →Battle Map: The Sunken Vault
DM OVERVIEW NOTES
- ◆The map is built to play as a slow descent from suspicious quiet into loud, waterlogged chaos.
- ◆Sound carries strangely through the chamber; whispered plans in one room can be heard as broken echoes in another if the party is careless.
- ◆Water levels can be adjusted mid-session to raise pressure. A sudden surge turns safe stone into difficult terrain and can cut off retreat.
Entrance Cavern
18 x 14 squares · Dim light from guttering oil lanterns hung on pitons and pale blue fungus along the cavern wall.
TERRAIN
- ◆A natural limestone shelf forms the entry point, ten feet above the main cavern floor, with a rope ladder hanging into the chamber.
- ◆Two smashed cargo skiffs lie on their sides and provide half cover for anyone crouching behind warped planks.
- ◆A stone causeway runs toward the vault proper, but several sections have cracked and dropped into waist-deep water below.
- ◆Collapsed support beams create a tangled choke point that Small creatures can slip through without squeezing.
HAZARDS
- ◆Slick stone: a creature that dashes across the wet causeway must succeed on a DC 12 Dexterity saving throw or fall prone.
- ◆Loose scree on the shelf can be dislodged; creatures directly beneath it take minor bludgeoning damage if someone climbs recklessly.
- ◆A hidden tripwire left by fleeing thieves drops a lantern basket, briefly creating fire on floating oil before the water smothers it.
DM NOTES
- ◆Use this room to foreshadow the guild's rushed escape: snapped lockpicks, a ledger page, and a single coin purse left behind tell the story.
- ◆The elevated shelf gives ranged characters a natural opening position, but enemies on the causeway can also pin the party in place.
- ◆If you want a stealth start, the roar of moving water grants advantage on the first group Dexterity (Stealth) check made here.
Flooded Vault Floor
24 x 20 squares · Patchy low light from floating lantern bowls, intermittent lightning-blue arcs from broken warding sigils, and reflections off the water.
TERRAIN
- ◆Black water covers most of the marble floor, ranging from knee-deep near the edges to chest-deep in the center channel.
- ◆Rows of iron deposit cages create lanes of broken sightlines; many doors hang open while others are twisted shut.
- ◆Three raised cashier islands sit two feet above the water and function as stable firing platforms.
- ◆A massive counterweight chain hangs from the ceiling where a chandelier once stood, allowing daring characters to swing across a flooded gap.
- ◆Scattered strongboxes drift slowly with the current and can be used as improvised floating cover.
HAZARDS
- ◆Electrified sigils: a creature that starts its turn in marked water near a broken rune plate takes lightning damage unless it moves out or disables the plate.
- ◆Hidden drop shaft: one five-foot square near the central dais conceals a broken drainage grate that plunges fifteen feet into rushing water below.
- ◆Strong current at the center lane counts as difficult terrain and can push unsecured creatures five feet downstream at the end of their turn.
DM NOTES
- ◆This is the main set-piece room. Keep the battlefield moving by drifting cover, shifting water, and enemies using cages to break line of sight.
- ◆A clever party can shut down the lightning hazard by tracing the silver inlay back to a cracked control box on a cashier island.
- ◆Treasure should be visible but inconvenient: jeweled lockboxes bob just out of reach, tempting characters into bad positions.
Inner Sanctum
14 x 12 squares · Low blue-white light from intact warding glyphs around the sanctum door and a steady golden glow from a cracked counting altar.
TERRAIN
- ◆A bronze vault door stands half open, wedged by a dead steel spar and scored with fresh thieves' tools marks.
- ◆The central floor is mostly dry on a raised mosaic dais engraved with scales, keys, and sunbursts of commerce.
- ◆Four narrow channels at the room's edges drain water away in a constant hiss, making the chamber feel unnaturally still compared with the flood outside.
- ◆Stone plinths display sealed reliquaries, bond scroll tubes, and ceremonial minting dies secured under glass bells.
HAZARDS
- ◆Sanctum ward backlash: forcing the reliquaries or tampering with the altar without the proper phrase triggers radiant damage and briefly seals the door.
- ◆Shattered guardian statue fragments animate when blood is spilled on the dais, creating a short-lived but violent complication.
- ◆The wedged vault door can be knocked loose, potentially slamming shut and splitting the party.
DM NOTES
- ◆Treat this room as the moral and narrative core of the adventure. The greatest prize is here, but so is the clearest evidence of who ordered the robbery.
- ◆The sanctum is a strong place for negotiation or betrayal because the water noise drops and every word feels deliberate.
- ◆If the session needs a climax, place the fence or the surviving crew here while the final ward fails one layer at a time.
NPC Profiles
Full backstory, motivations, and stat blocks for every character.
Mirelle "Latch" Voss
Half-elf · Rogue mastermind and thieves' guild fence
APPEARANCE
Mirelle dresses like a mourner who expects applause, wearing a rain-dark velvet coat over fitted leathers threaded with hidden pockets.
PERSONALITY
- ◆Measured and almost impossible to fluster in conversation.
- ◆Treats information as a currency more valuable than coin.
Flaw: She assumes everyone has a price and can miss the moment when conviction becomes dangerous.
Bond: Her younger brother is rotting in a debtors' prison, and every risky job she takes is meant to buy his way out.
KEY LINES
- “Easy now. The vault's already drowning; no sense adding your good judgment to the casualties.”
- “I did not rob this place. I merely know who is desperate enough to sell what was robbed.”
STAT BLOCK
- Deception +8
- Insight +6
- Sleight of Hand +7
- Shortsword +6 (1d6+4 piercing)
- Hand crossbow +6 (1d6+4 piercing)
Special: Exit Clause: When reduced below half hit points, Mirelle can take a bonus action to Disengage and move through flooded difficult terrain without penalty until the end of her turn.
Sister Ondra Flintmere
Mountain dwarf · Cleric of commerce and former vault chaplain
APPEARANCE
Ondra is broad-shouldered and square-jawed, with iron-gray braids wrapped in brass prayer rings stamped with old bank seals.
PERSONALITY
- ◆Blunt, disciplined, and deeply respectful of oaths.
- ◆Keeps a surprising tenderness for frightened clerks, guards, and other ordinary workers caught in grand crimes.
Flaw: She confuses protecting the institution with protecting the innocent and can become stubborn when those duties conflict.
Bond: Ondra swore over the vault keys that no sacred deposit entrusted to the bank would be lost on her watch.
KEY LINES
- “Mind your boots. This hall remembers every broken promise made inside it.”
- “Coin is only metal. Trust is the true treasure here, and trust is what was stolen first.”
STAT BLOCK
- Warhammer +6 (1d8+4 bludgeoning)
- Sacred Flame DC 14
- Guiding Bolt +6
- Insight +5
- Religion +6
Special: Seal of Appraisal: Once per encounter, Ondra brands one creature she can see; allies gain advantage on the first attack against that creature, and illusions on it briefly shimmer.
Kesh Reedfin
Goblin · Salvage diver, lockbreaker, and unwilling guild asset
APPEARANCE
Kesh is a wiry goblin with olive skin, a split left ear, and oversized diving goggles strapped permanently around his forehead.
PERSONALITY
- ◆Fast-talking and inventive under pressure.
- ◆Braver in water than on dry land.
Flaw: He panics when cornered and will betray nearly any plan if he thinks it buys him another breath.
Bond: Kesh wants enough money to vanish upriver with his older sister before the guild decides he knows too much.
KEY LINES
- “I was hired to open boxes, not drown in them. That distinction matters to me.”
- “Listen, I can show you which crates float, which plates bite, and which tunnel the crew used to run.”
STAT BLOCK
- Dagger +5 (1d4+3 piercing)
- Thieves' Tools +7
- Perception +5
- Stealth +7
- Swim speed 30 ft.
Special: Flood Sense: Kesh can identify concealed currents, unstable grates, and trapped lockboxes in water with a quick glance, granting allies advantage on one related check each round.
Dialogue Tree
Branching conversation with hidden hooks. Click any option to expand.
Mirelle "Latch" Voss
“Weapons low, voices lower. You're standing in a flooded crime scene, and I'm the only one here who knows which thief still has the ledger you want.”
Encounter Hooks
Five ready-to-run hooks packed with narrative tension.
The Ledger Eel
A pale, ribbon-thin eel slithers through the flooded cages with a wax-sealed scroll tube strapped to its side by silver wire. The creature was a courier trick used by the bank's clerks, and it panics violently when bright light or thunder magic hits the water.
The False Survivor
The party finds a soaked clerk huddled on a cashier island, sobbing for rescue. The 'clerk' is actually a guild cutpurse using stolen livery, and the longer the conversation lasts the closer their hidden partners drift into flanking positions behind the deposit cages.
The Air Pocket Witness
A rhythmic knocking echoes from beneath an overturned counting table trapped against the current. Under it is a terrified junior auditor sheltering in an air pocket, clutching a partial client ledger and the first clear description of the robbery's true patron.
Coins in the Current
A split strongbox spills silver into a fast-moving channel, and the sound draws everyone in the room at once. While the greedy scramble for coin, the current uncovers a rune plate that threatens to electrify half the vault unless someone abandons the treasure and shuts it down.
Sanctum Breach Countdown
Hairline fractures crawl across the inner sanctum glyphs as the vault's final protections fail. Each round the party spends arguing, looting, or healing advances the countdown toward a radiant backlash that will either seal the chamber or blow the bronze door fully open.
Session Recap Template
Fill in the blanks after each stream to turn the session into a community post, Discord update, or newsletter teaser.
- ◆Session __ of __: The Sunken Vault
- ◆Party on the job: ________________________________
- ◆Tonight's objective: ________________________________
- ◆Biggest reveal: ________________________________
- ◆Sharpest player move: ________________________________
- ◆Most dangerous complication: ________________________________
- ◆NPC who stole the spotlight: ________________________________
- ◆Loot, leverage, or clues recovered: ________________________________
- ◆Unfinished problem heading into next session: ________________________________
- ◆Cliffhanger ending: ________________________________
- ◆Community question for chat/comments: If you were in the vault, would you trust ________________________________?
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