The Forgotten Forge: A Free D&D 5e One-Shot Adventure
- Nick@Verse
- Sep 11
- 8 min read
This adventure is designed for a party of four 3rd to 5th-level characters and should take approximately 3-4 hours to complete. The core campaign can be found here.
Table of Contents
Adventure Summary
"The Forgotten Forge" is a classic dungeon crawl with an industrial, fiery twist. Deep within a mountain stronghold or a lost underground city lies a legendary forge district, silent for centuries. Once the heart of a mighty kingdom, it is now a dangerous, unstable ruin. The residual magic and immense heat have drawn volatile fire elementals, while the forge's automated golem guardians have become corrupted, attacking all who enter.
The adventurers are tasked with venturing into this hazardous zone to clear it of threats and restart the Great Anvil, a masterwork forge capable of creating legendary items. To succeed, they must overcome environmental hazards, battle enraged spirits of flame and stone, and solve the mechanical puzzle of the forge itself, all while a hidden danger may be lurking in the shadows. This one-shot is perfect for DMs looking for a combat-heavy session with opportunities for clever problem-solving and a tangible, rewarding conclusion.
Adventure Hooks
A passing reader needs a reason for their party to be here. Here are three distinct hooks you can use to draw your players into the adventure:
The Elder's Plea: A local Dwarven lord, guild master, or historian (such as Borin Silvervein) approaches the party. Their people have just reclaimed this area, but their forces are stretched thin. The Great Forge is a symbol of their heritage and a vital asset for re-arming their guards. They offer a handsome reward (e.g., 250 gp each and a choice of one uncommon magic item from the DMG) to any group brave enough to secure it.
The Treasure Map: The party discovers an old, partially burnt map in a dragon's hoard or a dusty library. The map shows a location marked "The Great Anvil" and contains frantic scribbles about a hidden alcove containing "Iron Fury," a weapon of legendary power, warning that the forge's guardians have "turned mad."
The Master Craftsman's Request: A renowned blacksmith (perhaps a contact like Thrain Goldforge) is desperate. Their own forge is insufficient for a special commission (perhaps forging a weapon for one of the PCs). They have heard legends of the Great Anvil, a forge hot enough to shape any metal. They will fund the expedition and offer their masterwork services for free if the party can clear the forge and make it safe to use.
Journey to the Forge
The path to the Old Forge District is not a simple walk. It’s a descent into the warmer, more volatile levels of the mountain.
The wide, stone-hewn corridors of the upper halls give way to narrower, soot-stained service tunnels. The air grows noticeably warmer, carrying the faint, metallic scent of ancient coal and cold iron. The silence is broken by the drip-drip-drip of water and the distant, unsettling groan of stressed rock. The path is littered with the debris of a long-forgotten conflict: rusted axe heads, shattered shields, and the occasional splintered bone.
Hazard: Unstable Tunnel. The party comes to a 60-foot-long section of the tunnel where the ceiling is fractured and held up by rotting wooden beams. A character who succeeds on a DC 14 Wisdom (Perception) check notices the instability.
To cross safely, the party must be careful. Loud noises, heavy stomping, or damaging a support beam will cause a collapse. Any character moving through the area must succeed on a DC 14 Dexterity (Acrobatics) check to move nimbly. On a failure, they trigger a minor rockslide, taking 2d6 bludgeoning damage and being knocked prone. If a character fails the check by 5 or more, or if a loud spell like Thunderwave is cast, the entire section collapses. Every creature in the area must make a DC 15 Dexterity saving throw, taking 4d10 bludgeoning damage on a failed save, or half as much on a successful one.
The Forge District: General Features
Once the party passes the hazard, they enter the forge proper. Unless noted otherwise, all areas in the forge district share the following features:
Light: The area is in dim light, cast by faintly glowing embers in scattered braziers and pools of molten slag.
Sound: A low, constant hum of geothermal energy permeates the area, mixed with the hiss of steam escaping from cracked pipes.
Smell: The air is thick with the smell of sulfur, hot metal, and ozone.
Heat: The entire district is uncomfortably hot. Any creature not resistant to fire damage must consume twice the normal amount of water per day.
Area 1: The Elemental Antechamber
This large, circular chamber served as the receiving area for raw ore and materials. Now, it has become a lair for creatures drawn to the heat.
You enter a vast, circular chamber with a soaring, vaulted ceiling lost in shadow. A network of rusted iron catwalks crisscrosses the space above. Below, the floor is a chaotic landscape of cooled lava flows, deep pits filled with glowing molten slag, and massive, overturned ore carts. The heat is intense, rolling off the slag pits in shimmering waves. Two vaguely humanoid figures made of pure, dancing flame coalesce from the largest pools of liquid metal, their bodies crackling with rage.
Creatures
Two Fire Elementals have made this chamber their home. They are fiercely territorial and view any non-fiery creature as an intruder to be incinerated.
Tactics
The elementals are intelligent and use the terrain to their full advantage.
They will use their Fire Form ability to move through the molten slag pits, gaining total cover and emerging next to vulnerable spellcasters or ranged attackers.
They will attempt to grapple characters and drag them towards the slag pits. A character starting their turn in a slag pit takes 4d10 fire damage.
They will focus their attacks on one character at a time, hoping to incapacitate them quickly. If one elemental is heavily damaged, it will retreat into a slag pit to hide before re-emerging to attack again.
Area 2: The Golem Workshops
A wide archway leads from the antechamber into a long hall lined with workstations.
This long hall is a picture of industry frozen in time. Stone workbenches line the walls, covered with dusty, half-finished projects: ornate axe heads, intricate shield bosses, and plates of articulated armor. Silent anvils stand like stone altars, their faces scarred from centuries of use. Scattered about the room are three humanoid figures made of carved stone, motionless and covered in dust. One clutches a massive stone hammer, another a pair of iron tongs. They appear to be statues of smiths at work.
Creatures
These "statues" are three Corrupted Forgeworkers. Use the Gargoyle stat block, but their appearance is that of Dwarven smiths carved from granite. They are constructs, immune to poison and psychic damage. They remain perfectly still until a creature moves more than 15 feet into the room or touches a workbench.
Development
The golems are single-minded, designed to protect the workshops. They attack intruders without mercy. A character proficient in smith's tools or masonry tools can use their action to make a DC 15 Intelligence (Investigation) check while within 5 feet of a golem. On a success, they spot a seam in the golem's construction where a power rune is weakly seated. The next attack roll against that golem has advantage, and a successful hit deals an extra 1d8 lightning damage as the rune shorts out.
Once the golems are defeated, the party can safely investigate the workshops. A successful DC 13 Intelligence (Investigation) check reveals a masterwork set of Smith's Tools and three flawless chunks of adamantine ore, each worth 50 gp.
Area 3: The Great Anvil Chamber
This is the heart of the forge, the final destination of the adventure.
The workshop hall opens into a truly immense cavern. In the center stands the Great Anvil, a block of obsidian the size of a wagon, covered in glowing, dormant runes. It sits before a colossal forge hearth built into the cavern wall, its maw cold and dark. A web of massive copper pipes and conduits snake across the walls and ceiling, all converging on the forge. A giant pair of bellows, large enough to be operated by a giant, sits to one side. The entire apparatus is silent, waiting for a master's hand to bring it back to life.
The Skill Challenge: Reigniting the Forge
The Great Anvil cannot be lit with a simple cantrip. It's a complex, magical machine that requires skill and coordination to reactivate. This is a skill challenge. The party must achieve 4 successes before they accumulate 3 failures. Each character can attempt one task per round.
Here are some examples of tasks the players could attempt:
Pumping the Bellows: The bellows are massive and heavy. A character can try to pump them, requiring a DC 15 Strength (Athletics) check.
Unblocking the Conduits: The pipes are clogged with centuries of debris. A character can try to clear them, requiring a DC 14 Dexterity (Thieves' Tools) or Strength check.
Deciphering the Ignition Runes: The sequence to activate the forge is written in Dwarven runes on the anvil's base. A character can attempt to read and follow the sequence, requiring a DC 15 Intelligence (Arcana) or History check.
Redirecting Magic Flow: A junction box of magical conduits is sparking erratically. A character can try to stabilize the flow, requiring a DC 14 Dexterity (Sleight of Hand) or Arcana check.
Kindling the First Spark: A character with access to a fire spell can attempt to provide the initial spark at the precise moment, requiring a DC 13 spellcasting ability check.
Consequences of Failure: Each failed check causes a setback. A failed Athletics check might cause a gear to snap, making the next Athletics check DC 17. A failed Arcana check could send a harmless but startling blast of energy through the room. If the party accumulates 3 failures, the system overloads, causing a small explosion. Each character must make a DC 14 Dexterity saving throw, taking 3d6 fire damage on a failed save. The system then resets, and they can try again, but the DC of all checks increases by 1.
Success: After 4 successes, the runes on the anvil flare to life. The forge hearth roars with brilliant blue flame, and the entire cavern is filled with a hum of immense power. The Great Anvil is operational.
Treasure: The Hidden Alcove
When the forge ignites, the intense light reveals a section of the wall where the stonework doesn't quite match. A successful DC 12 Wisdom (Perception) check uncovers a loose stone. Behind it is a hidden, lead-lined box. Inside is Iron Fury, a +1 Warhammer. An inscription in Dwarven on its handle reads: "Let this hammer be the fury of our mountain, and its secrets the key to our halls." A character who examines the hammer's head closely and succeeds on a DC 16 Intelligence (Investigation) check finds that the head can be unscrewed, revealing a hollow compartment—a perfect place to hide a secret message or key for a future adventure.
Optional Twist: The Assassin's Strike
This event is for DMs who want to connect this one-shot to a larger campaign of intrigue and betrayal. As the party celebrates their success, an Assassin (or a Veteran for lower-level parties) who was hiding in the shadows using a Cloak of Elvenkind makes their move. They are not targeting the party, but an NPC who may have accompanied them (like the craftsman from the adventure hook). Their goal is to prevent the forge from being used. This immediately launches a surprise combat round and reveals that a larger, more sinister force is at play.
Conclusion and Scaling the Adventure
With the forge lit and its treasures claimed, the party can return as heroes. They have secured a vital asset and may have uncovered the first clue in a much larger mystery.
For Lower-Level Parties (1-2): Replace the Fire Elementals with 4 Magmins. Replace the Corrupted Forgeworkers (Gargoyles) with 3 Animated Armors. Lower all DCs by 2.
For Higher-Level Parties (6-8): Upgrade the Fire Elementals to Salamanders. Upgrade the Corrupted Forgeworkers to Stone Golems. Add a Fire Giant who has been trying to restart the forge for his own purposes as the final boss in the Anvil Chamber. You could also have the optional assassin be a powerful Master Thief or Mage.
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