The Lost Library: A D&D 5e One-Shot Adventure
- Nick@Verse
- Sep 11
- 9 min read
Table of Contents
Adventure Summary
"The Lost Library" is an exploration and puzzle-based adventure that challenges players' wits as much as their sword arms. Deep within a forgotten corner of a stronghold or an ancient, buried tower lies an archive of immense knowledge, sealed away for centuries. Its guardians still patrol the silent halls, its magical defenses are still active, and its secrets are jealously guarded.
The adventurers are tasked with infiltrating this library to retrieve a vital piece of lost information. To succeed, they must first solve the riddle to gain entry, survive the magically animated defenses of the main hall, navigate a labyrinth of shifting bookshelves, and finally confront the ghostly head archivist to prove their worth. This one-shot is perfect for DMs who want to run a session focused on atmosphere, puzzles, and roleplaying, with strategic combat encounters mixed in. Check out our dwarven stronghold mega campaign here.
Adventure Hooks
Every quest for knowledge begins with a question. Here are three hooks to draw your players into the dusty halls of the Lost Library:
The Historian's Dilemma: A scholarly NPC (like Borin Silvervein) requires a specific piece of information to thwart a current threat—perhaps the true lineage of a suspected traitor or the historical details of a ritual needed to consecrate a holy site. The only known source is a specific tome, The Records of the Fallen Clans, located within the sealed and dangerous Lost Library. He offers a rare spell scroll (e.g., Clairvoyance) and 200 gp to each party member for its retrieval.
A Personal Quest: During their downtime, a player character with a mysterious past (perhaps an orphan, or one with a forgotten family history) is given a clue by a sage or a fortune teller: "The truth of your bloodline lies in the Archivist's Sanctum, beyond the shifting stacks." This makes the objective deeply personal and a powerful motivator.
The Rescue Mission: A young, ambitious scribe or wizard's apprentice went missing a week ago. Their master, a powerful but busy figure, fears they foolishly tried to enter the Lost Library to make a name for themselves. The master offers a significant reward (a +1 magic item for the party) for the safe return of their apprentice, or at least for discovering their fate.
The Riddle of the Entrance
The library is not secured by a mere lock. The entrance is a single, seamless slab of polished stone with no visible handles or hinges. In the center, etched in elegant script, is a riddle.
The stone before you is cold and smooth, offering no purchase. As your torchlight dances across its surface, glowing silver script fades into view, forming a question:"I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. To find my knowledge, first you must know me. What am I?"
The answer is "A map." When a character speaks the answer aloud, the script glows brightly, and the stone slab grinds silently into the wall, revealing the dusty archive within.
The Lost Library: General Features
Once inside, the entire library shares the following characteristics:
Light: The library is filled with a soft, magical dim light emanating from enchanted crystals embedded in the ceiling. It is just bright enough to read by but casts long, eerie shadows.
Sound: An almost supernatural silence pervades the area. It is so quiet that the slightest sound—a scuff of a boot, a whisper—seems deafeningly loud. This can be represented by giving creatures advantage on Wisdom (Perception) checks that rely on hearing.
Smell: The air is dry and thick with the scent of old paper, leather bindings, and a faint, ozone tang of dormant magic.
Dust: A fine layer of grey dust covers everything, preserving the scene as it was left centuries ago. Any movement will disturb it, leaving clear tracks.
Area 1: The Grand Reading Room
This is the first and largest chamber of the library, an impressive but dangerous space.
You step into a breathtakingly vast circular chamber. Towering bookshelves, at least fifty feet high, line every inch of the curved walls, their contents lost in the gloom above. In the center of the room, a dozen heavy oak reading tables with high-backed chairs are arranged in a circle, each with a closed book resting upon it. The sheer scale and silence of the place give it the air of a grand, forgotten cathedral dedicated to knowledge.
Creatures: Scrivener Swarms
The books on the central tables are not normal. When any creature moves within 10 feet of the tables, the books snap open, their pages fluttering like wings as they rise into the air. Four Scrivener Swarms attack the party.
Scrivener SwarmMedium swarm of Tiny constructs, Unaligned
Armor Class 12Hit Points 24 (7d8 − 7)Speed 0 ft., fly 50 ft. (hover)
STR | DEX | CON | INT | WIS | CHA |
6 (-2) | 14 (+2) | 8 (-1) | 3 (-4) | 12 (+1) | 6 (-2) |
Damage Vulnerabilities fireDamage Resistances bludgeoning, piercing, slashingCondition Immunities charmed, frightened, grappled, paralyzed, petrified, poisoned, prone, restrained, stunnedSenses passive Perception 11Languages —Challenge 1/4 (50 XP)
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny book. The swarm can't regain hit points or gain temporary hit points.
Actions
Whispering Scourge. Melee Weapon Attack: +4 to hit, reach 0 ft., one target in the swarm's space. Hit: 7 (2d6) psychic damage, or 3 (1d6) psychic damage if the swarm has half of its hit points or fewer. The damage manifests as a maddening cacophony of whispering voices and conflicting textual fragments that overwhelm the target's mind.
Tactics and Roleplaying
Mindless Defenders: The Scrivener Swarms are magical constructs, not living creatures. They fight without strategy or fear. They will not retreat. They will focus on the nearest creature they perceive as a threat, swarming them relentlessly until that creature moves away or the swarm is destroyed.
Exploit the Vulnerability: The most crucial detail for the DM to convey is their nature. Describe them as a "flurry of dry paper" or a "whirlwind of parchment." This should be a clear signal to the players that fire is a very effective tool. When they are hit with fire, describe a large portion of the swarm instantly igniting, the whispers turning to a papery scream as they turn to ash.
Environmental Interaction: The swarms are part of the library. Describe them darting between bookshelves, causing scrolls to tumble from shelves as they pass. Their "Whispering Scourge" attack isn't silent; the entire room should be filled with a disorienting, low-level hum of voices while the swarms are active, making it difficult for the party to communicate. A character might need to shout to be heard by an ally 15 feet away.
Half Health: When a swarm is reduced to half its hit points or fewer, remember to describe the effect. "The whirlwind of books is noticeably thinner now, its chattering whispers weaker but no less menacing as it continues its assault." This reinforces the swarm mechanic and lets the players know their attacks are having a tangible effect.
Tactics
The swarms are mindless defenders. They will target any creature making loud noises or using magic first. They will use their swarm tactics to surround a single character, trying to overwhelm them. Since they are made of paper, they have vulnerability to fire damage. A DM might also rule that a spell like Silence could disrupt their psychic attack, causing them to disperse or granting resistance to their damage.
Treasure
After the swarms are defeated, the party can inspect the reading tables. Most of the books are mundane collections of poetry and history. However, on the main lectern, a successful DC 14 Intelligence (Investigation) check reveals a book with a false bottom. Inside is a beautifully crafted Quill of Fluent Thought, a magic item that allows the user to write for up to 8 hours without needing ink. Once per day, the user can also use it to cast the Comprehend Languages spell.
Area 2: The Shifting Stacks
Three archways lead from the Grand Reading Room into the main body of the library: a dense forest of towering bookshelves.
The neat, open space of the reading room gives way to a bewildering maze of bookshelves. They are arranged in long, tight rows, creating narrow corridors that twist and turn. As you take your first steps inside, you hear a deep grinding sound. With a shudder, a massive bookshelf slides across the corridor ahead, sealing the path. The maze is alive.
The Maze Puzzle
This area is a dynamic environmental puzzle. The stacks magically rearrange themselves, making navigation a challenge. Here's how to run it:
The goal is to reach the door to the Archivist's Sanctum at the far end of the maze. The maze has three "rows" of shifting shelves between the party and the exit. To pass each row, the party must find the "control mechanism" for that section—a large brass lever set into the side of one of the bookshelves.
However, the area is not safe. Patrolling the stacks is a powerful guardian.
Creature: The Brass Sentinel
A Helmed Horror patrols this area. Describe it not as armor, but as a life-sized humanoid construct of polished brass and marble, its face a smooth, featureless plate. It was created to police the library and will move to attack any creature it detects.
The dynamic nature of the maze is key to this encounter. At the end of each round of combat, a section of bookshelves grinds into a new position. This can:
Block line of sight.
Provide total cover.
Separate party members from each other.
Open a new path to one of the control levers.
The party must fight the Sentinel while simultaneously trying to navigate the puzzle. A clever party might use the shifting shelves to their advantage, trapping the Sentinel or creating a clear path to escape and find the next lever.
Area 3: The Archivist's Sanctum
After navigating the shifting stacks, the party finds a single, ornate door made of dark wood and iron. It is unlocked.
This room is a stark contrast to the rest of the library. It is a cozy, circular office. A large, ornate desk faces the door, and the walls are lined with a few, very specific-looking shelves containing scrolls and leather-bound ledgers. A fireplace, its embers long dead, sits on one wall. The air here feels heavy, and a palpable sense of sorrow hangs in the air. Hovering behind the desk is a translucent, shimmering figure of an old dwarf with a long, spectral beard and the robes of a scholar.
Guardian: Loremaster Alerion
The figure is Loremaster Alerion, the spectral guardian of the sanctum. Use the Ghost stat block. He is not immediately hostile. When the party enters, his voice, dry as turning pages, echoes in their minds.
"For centuries, I have guarded this knowledge from the unworthy. From the power-hungry and the foolish. You are the first to reach this sanctum since the fall. State your purpose. Why do you seek to disturb this silence? Convince me of your worth."
This is a roleplaying encounter. The party must explain why they need the information. Alerion will ask probing questions.
"What do you intend to do with this knowledge?"
"Knowledge is power. How do I know you will not abuse it as others did?"
"Show me that you value knowledge not for what it can get you, but for what it is."
If the party is respectful, honest, and can present a compelling case (e.g., they need it to save lives, restore honor, or prevent a great evil), Alerion will nod slowly and point a spectral finger to a specific ledger on the shelf. If the party is arrogant, threatening, or clearly lying, his form will twist with anger, his face becoming a mask of fury as he shrieks, "You are not worthy!" and attacks.
The Lore Treasure
The ledger Alerion indicates is the Records of the Fallen Clans. It contains the detailed information the party seeks. Tucked inside the back cover of the ledger is the library's greatest treasure: the Tome of Foundational Lore. A creature that spends 48 hours over a period of 6 days or less reading this tome can choose one skill from the following list and gain proficiency in it: Arcana, History, Investigation, Nature, or Religion. Once the book is read, its magic fades.
Optional Twist: An Unwelcome Discovery
For DMs connecting this to a larger plot: as the party finds the Records of the Fallen Clans, they are not alone. A mind-controlled Dwarf (use Veteran stats) and two Giant Spiders crawl out from behind the bookshelves, sent by the campaign's villain to seize or destroy the records. The attack comes when the party is likely low on resources after dealing with Alerion, making for a desperate and frantic battle to protect their hard-won prize.
Conclusion and Scaling the Adventure
Having retrieved the knowledge they sought, the party can now make their way out of the library, its guardians either appeased or defeated. They have gained a powerful secret and a unique reward, but may have also tipped their hand to a dangerous, unseen enemy.
For Lower-Level Parties (1-2): The Scrivener Swarms are Swarms of Bats (dealing slashing damage). The Brass Sentinel is an Animated Armor. Loremaster Alerion is a Specter. Lower all DCs by 2.
For Higher-Level Parties (6-8): The Scrivener Swarms have resistance to non-magical weapon damage. The Brass Sentinel is a Stone Golem. Loremaster Alerion is a Wraith, accompanied by 2 Specters of his former assistants.
We hope your players enjoyed their quest for knowledge in "The Lost Library"! To see how this adventure fits into a grander narrative of betrayal and reclamation, check out our full campaign
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