Prison Beneath the Stones

Free D&D Encounter: Prison Beneath the Stones

Do you ever feel stuck when planning your next D&D session? Perhaps you’re tired of sending your players off into the woods with the same old bandit ambush trope, or they went in a totally random direction you didn’t expect, and now you’re scrambling for a surprise encounter to keep them busy until you can re-write your entire campaign. Well, we’re happy to introduce a new category called Side Quests! These posts are short, free D&D encounters (or other TTRPGs!) with corresponding maps that can be easily threaded into an ongoing or one shot campaign, allowing busy DMs to throw in a random encounter at the drop of a hat.


We are really excited to introduce these short encounters to you, and we would love to hear what you think of them! These Side Quests are provided free of charge thanks to the support on our Ko-fi page. Be sure to tag us when you use or share this side quest!

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For our first Side Quest, we’ll be exploring the hidden chambers beneath a seemingly idyllic glade. This encounter is perfect for travelers wandering the countryside, through the woods, or on a secret treasure hunt. Below, you’ll find a similar layout to what you’ll see in my DM’s Guild publications* : after a brief overview, we’ll break down the map by room, including any suggested encounters. You’ll also find our Homebrew Monster stats are at the end. Now, with that…please enjoy!

Prison Beneath the Stones

Overview: An enchanted prison lies beneath an idyllic glade, tended by a small circle of druids. Only a few remember the exact nature of their ancient ward, but they will defend it with their lives. A natural, well-trodden cave opening descends into the earth on the northwest side.

Plot Hooks

  • An unscrupulous baron hired a group of adventures to retrieve a treasure that is rumored to lie beneath the glade.
  • The party stumbles across the scene of a recent scuffle. A satchel hides under a rock or hangs haphazardly from a tree branch. Inside, they find a scroll describing a malevolent presence in a nearby glade that must be stopped at all costs.


  • Druids
  • Cultists
  • Wolves
  • Shambling Hulk
  • Poison Puff Patches


The glade is roughly 80 feet in diameter before tall trees cut off the sunlight from reaching the forest floor. A small fire pit lies in the middle of a ring of standing stones.

Standing Stones

Four of the stones have carved druidic glyphs concealed by moss and overgrowth. A successful DC 13 Wisdom (Perception) check allows the adventurers to spot them. These glyphs are the lock that prevents anyone from accessing the prison underneath the glade. There are corresponding glyphs carved into the massive stone doors. Each glyph represents a natural phenomenon, discerned with a successful DC 15 Wisdom (Nature) check or by anyone who understands Druidic.

When a creature exposes a glyph to its respective element, the corresponding glyph on the stone door underground will dimly glow. It’s even possible for adventurers to stumble into a clue if it suddenly started raining or if they arrive at night. When all four glyphs are lit, the stone doors will open. The adventurers can use magic to replicate the conditions needed to open the door. These glyphs are:

  • “Lux”, meaning “Light”. Depending on the preparedness of the party, anyone using the Daylight spell would cause this glyph to glow, though Light could be used in a pinch if the party has no other options at their disposal.
  • “Tenebris”, meaning “Darkness”. The Darkness spell is the obvious choice, but creative spellcasters could use Moonbeam.
  • “Imber”, meaning “Rain”. Create or Destroy Water could be used, or any spell that causes moisture.
  • “Ignis”, meaning “Fire”. Any fire-creating spell will work for this glyph.


The party’s size determines the number of Druids, Cultists, and Wolves below. These should be split into 3 groups: 

  • Several rotating druids guard the clearing and their nearby kin. These druids tend to patrol the surrounding forest with a bonded pack of wolves. 
  • One or two warm their hands over the small fire.
  • Another stands watch from inside the cave entrance.

Party Level 5 or 6: 2 Druids, 3 Cultists, 2 Wolves

  • 4 Members – (Medium) — (672 XP Per Player)
  • 5 Members – (Medium) — Add 2 Wolves & 1 Cultist (600 XP Per Player)
  • 6 Members – (Medium) — Add 2 Wolves, 1 Cultist & 1 Druid  (688 XP Per Player)

The Underground


D1. Cave Entrance

Rainwater collects into a small stagnant pond in the middle of the cave entrance. Footsteps wind around a corner to the left, leading to a basic sleeping mat and amenities hidden from the main room. Directly across from the aboveground slope is a set of thick 10 feet tall stone doors carved with druidic glyphs.

Stone doors: The doors are heavy, immune to damage, and locked by the glyphs from the standing stones outside (see Standing Stones). The doors slowly swing outward when the glyphs are all glowing. The magic binding the door is unaffected by Knock or similar spells.

D2. Threshold

A moldy odor permeates this chamber. Moss and other fungus hang from the four rusty armor sets stationed around the room. An altar sits across from the main doors. Patches of fungus grow heavily near the door to the right, while the leftmost door seems to be unaffected by the intrusive growth.


Altar: A leather bound book rests atop the altar; it has also succumbed to the mold overtaking this room. Its words are unreadable.


Armor Sets: These are normal sets of armor, though the moss has rendered all of it unwearable and entirely useless.

D3. Crypt

The air in this chamber still smells old, but it is free from the odor of mold in the last room. In the center of the room is a stone altar on which rests the bones of a long forgotten druid. The skeleton clasps a pristine sword between their hands. Their other vestments have long rotted away. Two stone statues depicting ankhegs sit on opposite ends of the altar.


Statues: The ankheg statues are traps that spray acid on any who step on the stone plate before the altar. The DC is 15 to spot the pressure plate. A spell or other effect that can sense the presence of magic, such as Detect Magic, reveals an aura of evocation magic around the statue. The trap activates when more than 20 pounds of weight is placed on the pressure plate, causing the statues to release a 20-foot cone of acid. Each creature in the acid must make a DC 13 Dexterity saving throw, taking 22 (4d10) acid damage on a failed save, or half as much damage on a successful one. Wedging an iron spike or other object under the pressure plate prevents the trap from activating. A successful dispel magic (DC 13) cast on the statues destroys the trap.


Corpse:  The corpse is holding a +2 Longsword in their grasp. A thorny key made of wood rests underneath the corpse and can be spotted by anyone standing next to the altar. This key is used to unlock the cell door in the guardroom (D4). There is nothing else of value in this room.

D4. Guardroom

Faint spores softly float in the air, and the floor contains more patches of fungus than stone. Leaning against the opposite wall is a large mass of fungus, moss, and gray flesh. Long ago, the original guardian stayed in this room as the final protector of the prison but became warped with proximity to the cell. The Shambling Hulk rises when it senses any character that enters the room and will attack ferociously. A few unusual patches of spherical mushrooms grow around the room as well.

Locked door: A sturdy wood and stone door covered in vines sits to the left of the entrance. This door is magically locked and cannot be opened unless the thorny key from the crypt (D3) is used. Once unlocked, the vines slowly retract and the door can be opened.


Party Level 5: Shambling Hulk (See stats below)

  • 4 Members – (Medium) — (725 XP Per Player)
  • 5 Members – (Medium) — (580 XP Per Player)
  • 6 Members – (Hard) — Add 2 Poison Puff Patch  (750 XP Per Player)


Party Level 6: Shambling Hulk

  • 4 Members – (Medium) — (725 XP Per Player)
  • 5 Members – (Medium) — Add 1 Poison Puff Patch (885 XP Per Player)
  • 6 Members – (Medium) — Add 4 Poison Puff Patch (775 XP Per Player)

D5. Prison Cell

A narrow set of stairs descend 10 feet underground. The stone floor at the bottom of the stairs crumbles into a pool of water. An earthen landmass sits above the water in the middle of the cell, and sitting upon it is a carved stone platform with a single deep green emerald on its surface. 

Neither the gem or the podium are trapped.


Shambling Hulk

The Shambling Hulk is a terrifying amalgamation of an arcane flesh construct and fungal overgrowth, developed from centuries of proximity to the prison cell beneath the glade. Mushrooms, creeping vines, and other vegetation cover the creature’s muscular body, creating an almost serene tableau despite its imposing appearance. The hulk hunches at a height of 9 feet but would easily reach 12 feet if it stood upright.

  • Large construct, neutral
  • Armor Class 15 (Natural Armor)
  • Hit Points 145 (18d10 + 55)
  • Speed 30 ft.

  • STR: 19 (+4)
  • DEX: 8 (-1)
  • CON: 16 (+3)
  • INT: 6 (-2)
  • WIS: 10 (+0)
  • CHA: 5 (-3)

  • Skills: Stealth +2
  • Damage Resistance: Cold
  • Damage Immunities: Lightning, Poison
  • Condition Immunities: Charmed, Exhaustion, Frightened, Paralyzed, Petrified, Poisoned
  • Senses Blindsight 60 Ft. (Blind Beyond This Radius), passive Perception 10
  • Languages: Understands Druidic but can’t speak
  • Challenge: 7 (2,900 XP)

Immutable Form. The shambling hulk is immune to any spell or effect that would alter its form.

  • Lightning Absorption. Whenever the shambling hulk is subjected to lightning damage, it takes no damage and instead regains a number of hit points equal to the lightning damage dealt.
  • Magic Resistance. The shambling hulk has advantage on saving throws against spells and other magical effects.
  • Magic Weapons. The shambling hulk’s weapon attacks are magical.


  • Multiattack. The shambling hulk makes two slam attacks. If both attacks hit a Medium or smaller target, the target is grappled (escape DC 14), and the shambling hulk uses Engulf.
  • Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: (2d8 + 4) bludgeoning damage.
  • Engulf. The shambling hulk engulfs a Medium or smaller creature it grapples. The engulfed target is blinded, restrained, and unable to breathe. The target must succeed on a DC 14 Constitution saving throw at the start of each of the hulk’s turns or take 13 (2d8 + 4) bludgeoning damage. If the hulk moves, the engulfed target moves with it. The hulk can only engulf one creature at a time.

Poison Puff Patch

These spitting fungal patches evolved in the guardroom, feeding from the otherworldly energy leaching from the prison cell. Each puff mushroom grows between 8 inches to 1 ½ foot tall, sprouting in 5 foot patches along the flagstones. The patches detect movement and violently spit globules of poisonous spores at the target. The Shambling Hulk simply ignores the spit on the rare occasion that it has to move.

  • Small plant, unaligned
  • Armor Class 5
  • Hit Points 3 (2d6)
  • Speed 0 ft.

  • STR: 3 (-4)
  • DEX: 1 (-5)
  • CON: 10 (+0)
  • INT: 1 (-5)
  • WIS: 3 (-4)
  • CHA: 1 (-5)
  • Condition Immunities: Blinded, Deafened, Frightened
  • Senses: Blindsight 30 Ft.
    • Blind Beyond This Radius
    • Passive Perception 6
  • Challenge: 1/4 (50 XP)

  • False AppearanceWhile the poison puff patch remains motionless, it is indistinguishable from an ordinary fungus.


  • Spit PoisonRanged Weapon Attack: +2 to Hit, range 10 ft., one creature. Hit: 3 (1d6) poison damage, and the target must make a DC 13 Constitution saving throw, becoming Poisoned for 15 minutes on a failed save, or is not poisoned on a successful one.

There you have it! From here it’s up to you to decide if you want to create a deeper story arc involving the druids, the emerald, or anything else you liked. We would love to know if you use this Side Quest, so please drop a comment here on the blog, on Twitter, Facebook, or Instagram to let us know how it went! Lastly, if you liked this free D&D encounter, consider checking out our longer campaigns and map packets on our Shop page,  as well as the rest of our Side Quests

Happy Side Questing!

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