Make your own megadungeon with Dungeon 23

It’s 2023, and many people in the tabletop RPG space have decided to do ‘Dungeon 23’ this year, an excellent challenge from Mothership RPG’s Sean McCoy.  

The principle is simple: make a 365-room megadungeon, one room at a time. What a great idea!

I’m a big fan of megadungeons, so I might try this. Here are some ideas for doing it well.

What came before

If you’re used to a more story-based approach to D&D, you might want to delve into the game’s history.

The two most famous megadungeons are Undermountain in the Forgotten Realms and the ruins of Greyhawk in the setting of the same name. Both are older than the game itself. Greyhawk was designed by Gary Gygax in the early 1970s, and Ed Greenwood first started writing about Undermountain back in 1966. Of course, the ur-dungeon before both of them is Tolkien’s Moria in The Lord of the Rings.

The 5e treatment of Undermountain is 2018’s Waterdeep: Dungeon of the Mad Mage, which I am currently running. The dungeon runs from 5th to 20th level – the only official 5e adventure to reach Tier 4 – and contains a whopping 23 levels to explore (plus the subterranean city of Skullport). It is an excellent example of a megadungeon.

Doing megadungeons well

What inspiration can we draw from examples like Undermountain? Here are ten ideas.

1. Come up with an over-arching concept. Undermountain makes sense because of its backstory: the whole thing is the creation of Halaster, the mad mage. What’s yours? Is it an underground city, an ancient temple, endless caverns in the Underdark, or something else. It’s fun to create a character who in turn created the megadungeon. A mad wizard is the obvious choice, but what about a demon lord, a dragon, or even some kind of deity?

2. Give each level a theme. Ideally, you should be able to sum it up in one sentence: ‘a battlefield of tunnels between drow and troglodytes’ or ‘an academy of magic designed to test its students’.

3. Levels get more difficult the further down you go. This is a fundamental principle of a megadungeon, and an important one. Obviously you want a range of challenges within each level – some easy, some deadly – but you don’t want your players to be overwhelmed or bored.

4. Use Jaquays techniques. This is a fabulous essay series by Justin Alexander which every DM should read. In essence, it boils down to a few techniques that keep your dungeon interesting: secret paths, loops, level connections, multiple entrances. (Jennell Jaquays designed many excellent old-school adventures, and her design principles are well worth studying.)

5. It’s not all about combat. In fact, one of the things I love about Dungeon of the Mad Mage is how many opportunities it has for exploration and social interaction. If you use the random dungeon tables in the Dungeon Master’s Guide, only half of a dungeon’s chambers will have monsters or NPCs. The rest are traps, hazards, puzzles, or otherwise unoccupied.

6. Use factions. There are so many examples of monsters in the Monster Manual that would work well for this: giants, demons, mind flayers, and humanoids of all sorts. One to three factions per level is about right. For bonus points, hint at the factions one or two levels before the players get there. For example, while exploring the arcane chambers, the players encounter a drow spy from the level below.

7. Combine the traditional with the unexpected. Caves of goblins and crypts of skeletons can become stale, so throw in something surprising now and then. Undermountain has a forest, a junkyard, a miniature castle, and even a gate to outer space. Mix it up.

8. Have a home base. In Dungeon of the Mad Mage, it’s the Yawning Portal, a famous tavern in the city of Waterdeep. But yours doesn’t have to be! It could be a fortress, a research facility, a desert oasis, or something else.

9. Keep treasure special. It’s easy to go a bit overboard with treasure in a megadungeon, and this can make treasure less special as a result. Be a bit stingy with magic items and go rich with detail when they are discovered.

10. Include memorable characters. Again, it’s not all about combat! You need villains, allies, rivals, mentors, even just comic relief. See what you can do with monsters you wouldn’t normally think of as ‘characters’. Could you have an awakened bear, a nothic with some of its memories intact, or stone golem that has become self-aware?

Above all, a megadungeon is sprawling, crazy, and a teeny bit silly by its very nature. Don’t take it too seriously. Keep it varied, keep it simple, and have fun.  

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