D&D General Megadungeons


It can be done, the question becomes "is it worth it?" Players that like a lot of exploration and hack-n-slash can play a mega-dungeon for a long, long time. Other players will tire of the endlessness of it, even if you have a plot woven into it.

The only time I did one the players regularly enjoyed (other than back in 1E, where they were the norm) was The Labyrinth campaign. The characters found themselves transported from their own world to an underground town surrounded by a seemingly endless dungeon. When they talk to the townsfolk, they find that everyone was brought here this way (there are no children born in the Labyrinth), and most decided to stay. Monsters never seem to enter the town, and there is a magical fountain that provides endless water and a tree who's fruit provides a full meal (equivalent to a ration in weight). According to legend, there is an escape somewhere in the Labyrinth, and if someone finds it, it will return everyone back to their home world. Supplies in town are limited, except for food and water, so the costs for everything else remains the same. There are 4 exists from the town, each dungeon section populated by a common low level monster type. Each of those areas leads to more areas, which eventually overlap. The campaign I did was in 3E and ran to level 10, but could have run higher (I ended it because I was tired of it).

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5e Rappun Athuk is about as mega as they come. I mean...huge.

Dungeon of the Mad Mage/Undermountain is very good as well. Not as grim, more tricks than traps.

Both kind of suffer lack of detail in places (due to their sheer size I suspect) but easy enough to fill in. Undermountain is also very easy to expand, doubly so if you have the two boxed sets.

Creating your own can be fun too. I rely quite a bit on random generator tables for everything from layout to contents. The 5e DMG has some great tools to do this - best since the 1e DMG (and in some places better IMO).

I worked on Rappan Athuk for 5e and can attest that it is absolutely huge and will also most likely kill characters.

The only advice I have about Megadungeons is: make each level reasonably sized, and make sure there's a clear theme for each level. So, you can have 5-10 rooms in a level, but more than that is going to make the players get a little lost (if that's your goal, have it be a labyrinth and you don't need an actual full combat map, instead use a flowchart with only one beginning and ending and each "room" a separate part of the flowchart).

I tried to run a megadungeon with maps so huge I didn't even bother trying to draw them out at the table; I just borrowed my FLGS' projector and put the maps on roll20 projected on the wall. They were so big that my laptop slowed to a crawl trying to render all of it.


Unfortunately, try as I might, I can't find the thread where someone asked about how to make a dungeon interesting and we brain stormed up a megadungeon with multiple layers.

Anyway, some advice...

Generally speaking a megadungeon will follow a certain pattern.

There is a Haven near by where the party can rest in relative security and get basic services like refills of consumables, cleric healing (including importantly remove disease/remove curse) and identification of magical objects. Secretly, some faction in the Haven has nefarious plans, but they won't reveal them just yet. There are one or more mentors, quest givers, or guides in the Haven that can reveal lore about the megadungeon to get the party going in the right direction, and help out when they get stuck. Quite often these turn out to be exactly the same as the faction with the nefarious plans. In the Haven are also links to a variety of sidequests, some of which may go to small dungeons or encounter areas unrelated to the megadungeon, and others may be quests in the dungeons themselves. Some of the most persistent quest givers early on are almost always the nefarious faction, which is often a cult trying to recover the Foozle or resurrect/free the Big Bad. Eventually, uncovering that the nefarious faction is nefarious may lead to side quests in the Haven itself, or in a nearby town. These side quests help break the monotony of delving in the megadungeon.

There is a ruined level or levels on the surface representing some sort of castle or mansion. Those ruined levels have been occupied by some sort of demi-human tribe, which will end up being fairly long running antagonists of the party.

There is an extensive basement/crypt/dungeon/arcane laboratory beneath the ruins, often divided in to multiple sublevels. The demihuman tribe may control part of these sublevels, but typically have walled off other parts of it out of fear of 'the wierdness' that controls much of the rest. 'The weirdness' and other hints provides clues to some ancient evil located deeper in the dungeon.

The basement level has several 'backdoors' or concealed exits/entrances that allow it to be accessed in a way that bypasses the demihuman tribe, and leads to various sublevels with varying levels of convenience. At least one of these entrances is blocked by 'the beast', a powerful predator feared by both the demihumans and the inhabitants of the haven.

There are slave mines which is the primary economic activity of the demihuman tribe, and from which innocents can be rescued. Both the mines and the basement provide access to the Upper Caves.

The Upper Caves are a maze of caverns loosely inspired by real world cave systems and containing a surprising number of large predators considering the relative lack of obvious food supplies. They are filled with hazards, dangerous terrain, and have magical weirdness in them.

Very near the connection between the Upper Caves and the Basement level is the Ancient Vaults. These are the source of all the weirdness and evil in the area. Initially, they are sealed and the means to open them is beyond the ability of characters at the time they are likely to find them. All the best treasure and worst monsters are in the Ancient Vaults, and this is actually the ultimate goal of the campaign where the foozle is hidden and/or the Big Bad is imprisoned, but any attempts to penetrate them early on will quickly run into some encounter which can be fled, but which is clearly and obviously vastly beyond the CR of the party.

Beneath the Upper Caves, usually accessible by descending The Chasm, is the Lower Caves. The Lower Caves represent the Lost World and is a dark fairy world filled with Impossible Things, and in classical D&D is part of the Underdark. The Lower Caves have a scale such that exploration of them essentially amounts to wilderness exploration. The Lower Caves themselves contain a number of villages representing different factions living in the lower caves, that can be won as allies with varying degrees of difficulty, thus providing a 'home away from home' for those exploring the lower caves. Often the villages have particular things that they want the PC's to do to maintain friendly relations with them, which sometimes is, 'Destroy the neighboring village', and often is 'Rid us of this thorn in our side' which can be anything from a troll to a dragon. The Lower Caves often have links to other areas of the Underdark in case the party wants to do further adventuring. If you want to be particularly helpful, the Lower Caves can also contain a Magic Portal, which allows quick travel between them and someplace on or near the surface.

Occasionally, the Lower Caves contain The Lost City, which is a megadungeon within a megadungeon. For now though, one megadungeon is enough.

Enrico Poli1

I suggest "Eyes of the Stone Thief", for 13th Age.
It's incredibile, the best megadungeon I know of.
Adaptable for 5e.

Really is a breathtaking One Unique Thing.


You don't have to design the whole thing before playing, but can build it level by level - especially if you include some sort of story device in which deeper levels aren't "unlocked" until the PCs complete some task or quest on the current level.

I'd also suggest using some version of a Random Dungeon Generator for inspiration. Even if you have a tightly thematic megadungeon, you will still get ideas for how to fill out each room, chamber, cavern, etc. And scour over other megadungeons, steal elements you like.

I think the most important thing is to mix it up - make the levels, rooms, chambers different and diverse. Make the entire structure have cool and interesting features. Give the players the sense that they don't know what's around the next corner, rather than always the assumption of the same "another room, another monster." Maybe they stumble upon a deep hole that seems to have no bottom; or a giant cavern of luminescent lichen that has psychedelic (visionary) properties and wants to lure them lotos-like into an immortal stupor; maybe they encounter oozes and slimes, goblins and troglodytes, drow and duergar exploratory parties, an ancient but kind old red dragon, a group of githyanki on a secret mission for their queen, deep gnomes enslaved by a mind flayer, etc etc.

Oh, and even if it is just a sprawling hack-and-slack fest, make sure is story - underlying themes, history, legends, myths. Maybe there are layers upon layers of history - that the structure itself was created thousands of years before by some unknown lost race that is believed to be extinct (or is it?). Maybe a crazy wizard commandeered it a hundred years before for his or her experiments (sound familiar?). Maybe there are factions of Underdark races vying for control, but also all seeking some kind of artifact. Maybe a famous adventuring party disappeared twenty years previously. Or take a different approach and have the PCs start at the "bottom," and have to fight their way out, level by level.

Have fun with it, and use your own sense of wonder as your guide. Build a megadungeon that you yourself would love to explore (as a PC, of course!). Oh yeah, and make sure there are always stray ends...passages left unexplored, if only hinted at. That sense of "Terra Incognita" brings a crucial element of mystery to the environment, and will help inspire the PCs to continue exploring.


A suffusion of yellow
I did a mega dungeon in one setting that was a vast modular structure that could be actively reconfigured

It consisted of a monastery whose catacombs were built over the top of an ancient cave system below which was a deep cavern which contained the sunken tomb of an ancient Vampire Lord who had a magic sword plunged through his heart before he was entombed in the deepest cave.

Later another section of the caves were used by bandits who are said to have dug tunnels linking the caves with the Castle of the local Baron (and leader of the smugglers) and out to the coasts. The smugglers tunnels were distinct from the caves but accessible

The Monastery was abandoned though after it was infiltrated by a cult who claimed that the Vampire Lord was infact the true king of the land before it was conquered by 'The Empire' and wished to pull the sword from his heart so they he could drive the Empire out and reclaim his home.

The cult started exploring the caves establishing caches in the deeper caverns but were eventually stopped when the Inquisitors lead by Cuthbert investigated and stamped the cultist out, burning many at the stake and chasing others into the deep caverns which the Inqusitors then blew up demolishing the area and collapsing the entrances. This means that the caves and tunnels are unstable and subject to collapse and changing configuration everytime they are used (that allows me to change up the maps and decide when new areas can be accessed)

The entrance to the caves was sealed with holy wards and a statue of Cuthbert was erected in the catacombs to guard the door. Soon after Pilgrims started to gather to pray to Saint Cuthbert and a small community of pilgrims has arisen around the edges of the monastery. Imperial Troops sometimes wander through as well, attempting to disperse the pilgrims and ensure than none of the cultist come back amongst their numbers

So an adventurer going to the Shrine will find
Layer 1 A community of religious pilgrims come to visit the Shrine of St Cuthbert, occassionally preyed on by bandits, goblins and Imperial guards looking for cultist
Layer 2 a abandoned and possibly haunted monastery with more cultist and bandits
Layer 3 Catacombs (which are always haunted) with traps, rats and the magically warded Shrine of Saint Cuthbert

The Sealed Door

Layer 4 abandoned, burnt out catacombs (undead)
Layer 5 the caves - a vast network, many collapsed and collapsing which means that they are difficult to navigate. Contain caches of survival items left by earlier explorers and possibly home to cannibal cultist
Layer 6 the smugglers tunnels - accessed from the caves and used by smugglers and bandits
Layer 7 the deep caverns - far beneath the caves are a series of deep cavernous spaces
Layer 8 the ancient tomb - in which lies the Vampire Lord with a magic sword through his heart

I’m planning a mega dungeon for my own ‘D&D 5E / Basic Fantasy game.

I’m actually already using Stonehell, but I will
be expanding it and adding my own elements. Eventually, my additional levels will interact with the existing power structures and become one thing.

I would recommend looking at Stonehell as a guide or example. It is quite possibly the best published mega dungeon available. It combines a detailed background with a high level of usability in-play and a lot of variety/themed levels. It is also very modular... you can literally pull a quadrant out and use it as a stand-alone or add it to your own dungeon.

A good starting point may actually do what I am doing... take an existing product and add your own creations. It’s easy to erase a wall or add a secret door.


As I've never seen this (though have heard of it on various occasions) dare I ask, what's wrong with it?

The best start of this answer involves how the book was made, which was that that divided the dungeon into like 25 (36? Some number) sections, assigned a few monsters of appropriate CR to the sections until they'd separated out basically the whole SRD, and then asked a bunch of authors to individually work on the sections, sewing the resulting maps together like a patchwork quilt from some middle school arts project.

The result of this design by committee was uninspiring in both its grand design and its details. The individual sections were fairly monotonous with the same sort of monster reoccurring several times. There wasn't much in the way of exploration. There were few surprising connections to make, no sublayers to discover, no real sort of twists and turns to take beyond well, left/right. There wasn't a particularly cool overall layout to the map, nor was their particularly cool layouts to the individual map pieces. Thematically the whole thing was supposed to literally be some sort of dungeon to trap monsters in.

By abandoning the haven/delve format players I think lose any particular feeling of agency. It's just a labyrinth of left or right choices with random monsters stuck higgledly-piggledly in the way. And by abandoning verticality, you lose the ability to make hubs, shortcuts, and so forth to reduce travel time, to say nothing of just being monotonous to imagine.

Honestly, starting with the random dungeon generator in the back of the 1e AD&D DMG as a guide, I'd expect someone to develop a more fun and interesting mega-dungeon.


Unfortunately, try as I might, I can't find the thread where someone asked about how to make a dungeon interesting and we brain stormed up a megadungeon with multiple layers.

You may be thinking of this discussion Gabor "Melan" Lux posted in 2006?: Dungeon layout, map flow and old school game design or perhaps this one?: Would these maps make for a fun dungeon adventure? ??

Other good discussions about mega-dungeon design are largely off-site:



You may be thinking of this discussion Gabor "Melan" Lux posted in 2006?: Dungeon layout, map flow and old school game design or perhaps this one?: Would these maps make for a fun dungeon adventure? ??

Other good discussions about mega-dungeon design are largely off-site:


No, those are good threads, but not the one I was thinking of. The one I was thinking of, a DM had started a campaign with some vague ideas, and he was wanting to know how he could use what he'd developed so far as the basis for a large megadungeon that could be the focus of the whole campaign.

Tyler Do'Urden

Soap Maker
A few others:

The Emerald Spire (Pathfinder)

Tomb of Abysthor (another Necromancer 3e Module - about a third the size of Rappan Athuk at 8 levels/sublevels, but still pretty mega in my book, and a bit more digestible. Designed to take PCs from 2nd to around 8th or 9th level).


The High Aldwin
Has anyone ever created a megadungeon before, like a place where the characters enter the dungeon at level 10 and come out level 13?
The biggest dungeon I created was called "the Ultimatum". It was 88 levels and over 2000 encounters. I made it in high school over a year for 1E. I think it might be in the basement someplace with my high school stuff. It would be a beast to convert to 5E, but if I find it maybe I will make it a winter project. :)
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