Many people believe even basic maps enhance the play experience in DnD. This is especially true for online play.
Here's my take: if you can run a better game with a map on hand, then it’s a good idea to have a few of them ready!
With this DnD Tunnel Map I’ve dubbed “The Underground Mycotic Railway”, you can create an eerie adventure that will keep your party on their toes.
So if you want to take your DnD players deep into the mysterious underground, you’ve stumbled in the right place!
If you’re stumped on encounter ideas, we’ll also explore some unique encounters for different sections of this tunnel map.
Let's craft an unforgettable dungeon crawl for your next game!
DnD Tunnel Map: Rooms & Encounter Ideas
If you feel like you’ve hit a dead end with building encounters, you can use the following ideas and descriptions for inspiration.
1) Entrance Tunnel
Tunnel Environment Description: An overgrown railway tunnel emerges from the dense foliage, its entrance obscured by creeping vines and tangled roots. Faint beams of sunlight filter through the canopy, casting dappled shadows upon the moss-covered tracks. Strange symbols are etched into the crumbling stone walls, while distant echoes of water droplets fill the air.
Encounter Ideas (Exploration):
Clue Discovery: Characters find an ancient tome with diagrams of the railway and hidden dangers.
Ore Vein: Rare ore embedded in the walls, but mining it triggers a structural collapse.
Remains/Signs of Trouble: A partially buried skeleton with a journal warns of something lurking deeper within.
2) Fungal Passage
Description: The air thickens with humidity, and bioluminescent fungi coat the tunnel’s walls, their eerie glow casting long shadows.
Obstacle Encounter Idea:
Fungal Spore Trap: Stepping on a patch of fungi releases spores, causing hallucinations or poisoning unless players navigate carefully.
3) Abandoned Mining/Tunneling Operation
Description: Old, rusted mining equipment is scattered around a collapsed section of tunnel, with overturned carts and cracked wooden supports.
Social/NPC Encounter Idea:
Ghostly Miners: Spirits of former miners, cursed to roam the tunnels. They’ll offer information about the dangers ahead in exchange for proper burial rites.
4) Broken Bridge: The Poisonous Lake
Description: The tunnel opens up into a cavern with a crumbling bridge that spans a murky, poisonous lake. Thick fumes rise from the water, and the faint sound of something moving beneath the surface puts everyone on edge.
Combat Encounter Idea: Depending on how the party crosses the bridge, they may face one of the following threats:
Monster | Description |
Toxic Lake Serpent | A serpent emerges from the water, spewing acid in wide arcs across the bridge. |
Venomous Fungus Golem | A massive golem made of toxic fungus rises from the lake, attacking intruders. |
Lurking Ooze | A large ooze monster drips from the bridge's edges, trying to engulf the party. |
5) Blocked Antechamber
Description: Ahead, the passage is blocked by thick, intertwining vines. Strange symbols glow faintly on the walls, hinting at an ancient ward.
Puzzle Encounter Ideas:
Light Puzzle: Players must light torches in a specific sequence to dissolve the vines.
Word Riddle: A riddle etched in the stone reveals the secret word that will part the vines.
Symbol Matching: Characters need to match glowing symbols on the walls with runes found earlier in the tunnel.
6) Boss Chamber: The Fungal Blight
Description: The final chamber is vast, with a large pool of dark, corrupted water in the center. The walls pulse with fungal growth, and the air is thick with spores. The Corruption Pool radiates malevolent energy and ripples hint at something lurking within.
Boss Encounter Idea: (Corrupted Treant)
Fungal Blight Boss: A massive fungal creature rises from the pool, drawing power from the poisonous water to fuel its devastating attacks. It can create spore clouds, poison players, and summon fungal minions from the surrounding walls.
Tip: Use the Treant stat block as inspiration for this and make it chaotic evil. Reflavour some attacks to poison damage and allow it to summon corrupted Treants or Blights as minions.
Expanding The Underground Tunnel
Looking to expand the adventure beyond this tunnel into another adventure?
I left the northeast area of the map open alone for that reason. Here are some ideas for future session content:
The Northeast Railway Continues: The tunnel stretches deeper, revealing a more dangerous, unexplored region.
Collapsed Exit: The way forward is blocked, forcing players to find another route - or a way to clear it.
Abandoned Facility: The party stumbles upon a forgotten mining complex, processing plant, or research facility overrun with strange creatures.
Feel free to use another map I made such as the Swamp D&D Castle Map for your home games!
Conclusion
This DnD Tunnel Map offers countless ways to engage your players in a thrilling underground adventure. Whether you're using it for a one-shot or incorporating it into a larger campaign, the encounters here are sure to inspire.
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How will you use this map in your D&D game? Leave a comment and let me know.
(Note: Map made in Dungeon Draft)