Need a quick coastal dungeon? You can follow this five-step random generator to create an entirely random dungeon shell you can fill in and personalize until your heart's content!
The entries are deliberately somewhat vague to allow more GMs to use them, as they’re open to incorporating varieties of monsters with varieties of challenges on most outcomes.
While these reference monsters from D&D, the results can work at most fantasy RPG systems beyond D&D.
1. Where is the Dungeon?
The following table provides you options for where the dungeon is within a coastal environment:
Coastal Dungeon Location Table
| d10 | Location |
|---|---|
| 1 | Overlooking a sprawling beach covered in wreck debris |
| 2 | Nestled on a dense jungle island protected by shoals preventing easy approach |
| 3 | Centered within a flourishing bay complicit trading community |
| 4 | Atop a steep rocky cliff home to a ship graveyard below |
| 5 | Where a river meets ocean in the remnants of a destroyed city |
| 6 | Connected over smaller islands with narrow shallow water pools between them |
| 7 | Built within a massive ocean-side cave crusted with unnaturally flourishing barnacles |
| 8 | On a head above a cracked inlet leading to a discreet dock for smaller vessels |
| 9 | Half-submerged in the coastal waters below a large stone arch jetting from the land |
| 10 | Built within a lagoon overrun with oversized wildlife |
2. What is the Dungeon’s Purpose?
The following table determines the builder’s purpose for this dungeon:
Coastal Dungeon Purpose Table
| d8 | Purpose |
|---|---|
| 1 | The dungeon provided a refuge for a band of pirates who were tracked and slain here |
| 2 | The dungeon was a hideaway smugglers used to stash illegal goods |
| 3 | The dungeon was a facade hiding a ritual cult worshiping a deep sea monster |
| 4 | The dungeon offered a necromancer access to aquatic corpses for terrible tests |
| 5 | The dungeon doubled as a black market for traders from across the waters to barter |
| 6 | The dungeon was perfectly located to absorb storm energy into a disastrous spell |
| 7 | The dungeon is a temple dedicated to a deceased storm god, ruined by its replacement |
| 8 | The dungeon protects a rare buried treasure that calms the nearby waters |
3. What is the Dungeon’s Structure?
The following table determines a general structure you can use to build your dungeon:
Coastal Dungeon Structure Table
| d8 | Structure |
|---|---|
| 1 | A decommissioned lighthouse overtaken by its new inhabitants |
| 2 | A sturdy church with boarded windows and a shoddy crumbling chapel leaning over it |
| 3 | A cave network accessible through a quick trip through a fetid waterway |
| 4 | A salt-crusted fort ruling over the surrounding overgrown and ruined plantations |
| 5 | A alchemist laboratory powered by the winds and rains local to the region |
| 6 | A campsite around a mysterious series of obelisks engraved with mysterious sigils |
| 7 | A fortress composed of dozens of ships cobbled together into a massive lair |
| 8 | A settlement of fishing huts and docks sprawling over the area |
4. Who Currently Resides in the Dungeon?
The following table determines what kinds of creatures reside in the dungeon:
Coastal Dungeon Creatures Table
| d20 | Creatures |
|---|---|
| 1 | Humanoid pirates using the lair as lodging between raids |
| 2 | Blue kobolds who stash their treasure tributes for their blue dragon overlord here |
| 3 | Goblins, having claimed this lair for their clan and will defend it tooth and claw |
| 4 | Sea elf scouts, who initially used it as a temporary shelter on a reconnaissance mission |
| 5 | Undead sailors bound to the region after meeting their terrible fate on the nearby ocean |
| 6 | Fey, who lure seafarers to their demise for their own entertainment |
| 7 | Demons summoned initially to take the lair who killed their summoner in their attack |
| 8 | Devils who enslave weary travelers in exchange for what they need to continue living |
| 9 | Celestials bound to protect the region who have slowly gone mad from their isolation |
| 10 | Dwarves seeking riches below the waves |
| 11 | A blue dragon who uses the lair to stash their massive trove of treasures |
| 12 | Constructs damaged from their proximity to the waters and salt |
| 13 | Gnomish storm chasers who stumbled across a deep monster that took their free will |
| 14 | Water elementals feeding on the magical power drawn to the lair |
| 15 | Giant beasts enhanced with an archdruid’s protection spells to keep society from further harming nature |
| 16 | Aquatic and amphibious plant creatures that feed on trespassers |
| 17 | Sahuagin or other fish-folk creatures using the lair as an outpost between sea and land |
| 18 | Oozes formed from brine and water overrunning the lair and dissolving creatures within it |
| 19 | Deep aberrations using the dungeon to perform dark rituals to awaken a world-ender |
| 20 | The dungeon is eerily empty, protected by magical and mundane traps |
5. What Rooms Are in the Dungeon?
Consider either rolling as many times as you’d like ahead of time to plot out the dungeon, or rolling as the players progress through where the new doors may lead. There are two options: an ordinary rooms table, for when you want the players to explore some mundane options, and extraordinary rooms for when you want to spice things up a bit.
The following tables can be rolled on to determine what rooms the players encounter as they progress:
Coastal Dungeon Ordinary Rooms Table
| d12 | Ordinary Room |
|---|---|
| 1 | Insulated cold storage containing preserved fish and other spoils of the sea |
| 2 | Dining chamber, with tables and seats fashioned from crates and barrels |
| 3 | Housing and bunks lined with hammocks along the walls over chests of clothes |
| 4 | Armory with sets of both aquatic and above-water weapons for fighting both fronts |
| 5 | Cells, damp and slightly flooded, with worms and sea critters skittering in the sand |
| 6 | War room with a central map of the water it's on with faction flags marked all over |
| 7 | Prayer room with small shrines to numerous gods of sea, travel, thievery, and more |
| 8 | Navigator’s chambers, clean and propper with navigation tools for plotting sea travel |
| 9 | Dry storage with dried goods on lifted platforms and insulated in large barrels |
| 10 | Council chamber with central seats around a trapdoor dropping the guilty below |
| 11 | Slaughter room with fish guts and larger sea monster hanging on chains and hooks |
| 12 | Map room, adorned with wax sealed cases to preserve precious paper charts |
Coastal Dungeon Extraordinary Rooms Table
| d8 | Extraordinary Room |
|---|---|
| 1 | Ritual chamber to a tentacled figure, stone mouth agape and bloody |
| 2 | Storm-punk laboratory with equipment made to harnesses the winds and rain for power |
| 3 | Fighting pit around a water tunnel where prisoners are fed to beasts of the deep |
| 4 | Hatchery full of moist eggs from amphibious monsters nestled in cozy baskets of sand |
| 5 | Puzzle room of magical rising water that drowns the denizens if they can’t solve it |
| 6 | Deep-sea dock accessed by stairwell going below with a magical submersible |
| 7 | Well for the dead, each in a weighted casket in the waters marked with a floating marker |
| 8 | Pool of water used to teleport from one coastal lair to a paired dungeon |
