Let’s Build a Low-Prep Mega Dungeon: Part 2

Plots and Copying Someone Else’s Homework

Cartography by Dyson Logos

So, another week, another missed Mouse Guard report, this time due to a family emergency. Our next session is booked, however. We will return to the Guard next week!

← Read Part 1 | Read Part 3

Welcome back! Last time I covered some basic things we could do as we prepare our low-prep mega dungeon. This time, we’ll go over some more specifics; an overall plot and how we can hack an existing module to fit our needs.


I can’t get enough of games like Dark Souls and Darkest Dungeon — they exemplify the best qualities of a great dungeon delve, not only because they are challenging, but also because they tease out their plots and lore in a way which makes you want to keep exploring, even though you’re getting killed all the time. Part of that intrigue comes from the fact that the stories aren’t your standard fantasy tropes. There might be dragons and zombies, but they still subvert our expectations in interesting ways. With that in mind, I think one of the most important things our mega dungeon needs is a good, creepy, hook to get the players interested. Lovecraftian themes have been in vogue for a while, and I see no reason not to continue the trend.

Now, horror and dread are difficult to build into a game like Dungeons & Dragons. For one, the system just doesn’t support these things very well. D&D wants you to hit things on the head to get their juicy experience, and true horror often rewards combat with an untimely end. So rather than try to scare the players, we should be interested in showcasing how wrong and weird things are in our game.

What might that look like? Well, a few weeks ago, my players and I got together and talked about what they thought the world was like. They decided on a high fantasy, high magic setting; something along the lines of the Eberron campaign setting. In this world, magic can be taken for granted in many places, and most “human-like” races are fairly prevalent. The more monstrous races; dragonborn, tieflings, anything in Volo’s guide; are more mysterious and rare.

That sounded good to me, but then I watched the WebDM “elves” video, and got an idea. In the video, the hosts discuss the idea of elves — who are effectively immortal — being completely aloof from the cares of the world. After all, if you live 600 years, any human civilization is going to be mostly inconsequential to you. What if most “magical” peoples are somewhat common in our world, with the exception of the elves? Maybe all of the “elves” in our world are something closer to half-elves; or maybe other elves (wood elves, drow, etc) exist, but the high elves don’t. What happened to them? Perhaps these elves were masters of the arcane, and the remnants of their civilization are what explain (and power) the mundane magic the people who came after utilize.

Sure, this is a tried-and-true trope, but that just means we get to subvert it later. If adventuring is an accepted occupation for people who venture into ancient dungeons to retrieve items of power, which are then dismantled and used to power society at large, it gives us a good jumping off point. It’s a good start, but it isn’t very creepy or dreadful. Time to amp it up.

In a remote region of the world, people are having trouble sleeping. A plague of nightmares has descended upon the area; preventing the local population from getting a solid night’s sleep. If this was an area where the “magical revolution” was slow in coming, an population who can’t sleep is a population who can’t work. No one knows why the nightmares assault them, but everyone generally agrees it probably has something to do with the ancient elven complex rumored to be underneath the sea cliffs. In fact, it’s common knowledge around these parts that there’s some kind of haunted or cursed dungeon on a rocky strand nearby; all you have to do is look for the pillars, jutting out like broken teeth from the cliff, and descend the wall to the entrance…

I think this hook is good enough to get us going, and it will give us plenty to work with as the characters uncover the plot while moving through the dungeon; where are the nightmares coming from? What did the elves do to cause this? Why have the disappeared, and what did they leave behind? Of course, when I say “uncover,” I really mean “come up with interesting ideas we can then use ourselves, which will make them feel clever.”


Now that we have a general hook in place, we need to start working on the actual dungeon! While we will definitely need some kind of overall map for our mega dungeon (one which shows the major areas, and how they flow into one another), I’m not convinced we need it right away. After all, we’re trying to do a low prep campaign here, and I don’t want to build more than I need to. So instead of worrying about that, let’s think about getting a good “front door” for our mega dungeon, and go from there.

As much as I love building dungeons from scratch, the fact is that I don’t really have time to do that any more. Luckily for me, there are other people who are happy to do it! Looking through the various modules I’ve run over the years, one sticks out as being almost perfect for us: the Sunless Citadel. Originally written for D&D 3rd Edition, I think it makes an excellent introduction to the game, as well as a fantastic “first level” to a mega dungeon. There are even unmapped passages leading deeper underground already built into the adventure. Even better, it was recently reworked for 5e as part of the Tales From the Yawning Portal book. So am I going to steal someone else’s homework? You’re damned right I am!

Alas, Sunless Citadel isn’t just right for our dungeon out of the box — it’s just not weird enough. As written, the module involves kobolds and goblins fighting over a lost citadel, which was dedicated to a dragon. In the background of this, an evil druid is doing some mildly evil things, and working with the goblins towards a somewhat ambiguous end. Frankly, I’ve always been a little underwhelmed by the meta-plot of the module, but that’s ok! It will be easy to bend things a little to our needs.

I think the first thing we’ll do is take out the goblins. Every beginning adventure ever seems to begin with some kind of goblin-esque enemy, and I’m frankly bored with them. Consulting the Monster Manual, we can pretty quickly locate a more suitable, Lovecraftian stand-in; the Kuo-Toa. This race of insane fish people is perfect for us, and they offer a similar challenge to the goblins. Perhaps they’ve been drawn to the ancient dungeon because of the weirdness happening deeper inside. In fact, I think our evil druid should probably be the leader of some kind of cult, dedicated to worshipping the twisted tree-like structure at the bottom of the citadel.

In the default module, this tree was where a vampire had been staked, which had corrupted the area around it. That’s ok, but not weird enough. I think instead of the Gulthias Tree, we have some kind of twisted, obscene growth; the result of some of the weirdness from deeper underground seeping up to the surface. The evil druid and some other human cultists tend the tree and worship it, and the Kuo-Toa revere the thing as an appendage to their god. The fish-people also look to the druid and his cultists as prophets of some kind, and all of them are pushing back against the kobolds, who have recently entered the citadel, hoping to take it for themselves.

Excellent! Now we’ve not only made the module more thematically appropriate for our plot, but we’ve also maintained the competing factions within the citadel. This will give our players opportunities to role play, as well as kick down doors and bust heads.

A few more steps remain. First, I went through the Sunless Citadel and made some notes. Anywhere the module puts some goblins, I dropped either some Kuo-Toa or cultists. I also made notes to replace all of the dragon motifs with weird, worm-like things (what were the elves doing here?). I updated the twig-blights; keeping their stats, but making sure I describe them less as animated plants, and more as tumorous, fleshy things covered in bark-like chitin.

Lastly, I explored the hooks suggested by the adventure, and settled on how we can get the players immediately involved — a previous group of adventurers went into the citadel and failed to return. Assuming they are dead, one of the adventurer’s cousins has come to town, hoping to retrieve a magic signet ring so that they might inherit the nearby family estate. They will send our characters into the dungeon to retrieve it, and hopefully put an end to the nightmares plaguing the region. This is a double bonus, as not only will it give the characters an immediate incentive to play, but it also could potentially provide us with another location; a haunted mansion. As an alternative, we can make one of the characters the cousin in question, hoping to retrieve the family ring and take the estate for themselves.


I think we’re off to a great start! The citadel should keep our players occupied for at least a few sessions, which will provide plenty of time, ideas and hooks for us to implement later. After the characters have played a session or two, we should have what we need to build out some plots and clocks, which we’ll use to track the world as the characters move through it.

I hope you’ve found this useful, and that it helps you to start building your own low-prep mega dungeon. As always, I appreciate any feedback you’d like to give. Until next time, happy delving!