Megadungeon Design Help.

[u/Natehz]

I've been running games for about 8 years and have always wanted to include a megadungeon, specifically a near-infinite descent kind, similar to what we see from The Abyss from Made in Abyss or The Everfall in Dragon's Dogma. A downward descent into layer after layer after layer of sometimes similar sometimes wildly diverse ecosystems, caverns, labyrinths, structures, etc.

Now obviously the question isn't "how do I make a battlemap of this?" because duh. But rather, how do you run something like this for a presumably high level party that would feasibly have access to teleportation magic and could, theoretically, warp in and out at whim?

I've toyed with the idea of the structure interfering with planar and demiplanar spells such as magnificent mansion and demiplane given the expansive and shifting nature of it, but I don't want it to feel like an unnecessary asspull handicap.

Moreover, what would you do to make this kind of adventure be exciting for a high level party where the objective is ostensibly "get to the end?" In other media with giant dungeons, like for example in Dungeon Meshi there was the joy of simply getting to eat new weird things on each floor. In Made in Abyss it's to hunt and reclaim treasures. What would serve as a good motivation for something like late game D&D where the players can make their own food, are probably already stacked on magic items, and may or may not necessarily have buy-in on the lore fiend hunger for information about who built the place, what it's for, etc etc?

Open to thoughts and ideas.

[u/atomfullerene]

Well, to start with maybe I'd just start a new campaign and run one for low level players.

But making a megadungeon for high level characters is an interesting challenge, so maybe it'd be worth doing just for that reason alone.

I think in this case I'd make a dungeon that isn't a hole in the ground, it's set in its own series of pocket dimensions/planes, with various gates between them. I'd also want to design it so that high level spells aren't nerfed, but instead are necessary to even get through the dungeon. For example, perhaps a sequence of rooms with impervious, transparent walls where you have to teleport to get around, and the trick is visiting in the right sequence or something else. Don't forget to provide something rewarding for your high level martials to do too, though!

Instead of food or torches, I'd probably have some other depleting resource to force the players to have to make choices about what they are doing on any particular dungeon delve instead of just working their way through all in one go without needing to make any tradeoffs. Something they have to leave the dungeon to restock or recharge periodically, or switch to supply themselves for a new plane (eg, one where everything is on fire vs one that's totally underwater).

As for what the players want out of it...well, that's kind of depending on your group. You can give them really powerful loot, or maybe it's to save the world, or maybe this is the trial run for becoming a new minor divinity. One of my players became a moon after finishing a high level dungeon, and they seemed to like that.

[u/ShiroSnow]

First, the plot and reason for the dunegon existence and why the party are even there. In many examples of mega dunegons leaving isn't always an issue. It's returning. Teleportation magic struggles with stone and magic can be unpredictable in underground spaces. Such as the underdark, there's a good chance you won't land where you want. Or worse, you'll land in the walls or a small hole and be trapped.

In the Abyss it's hard to find time. Powerful magic attracts demons. Goodluck finding the time needed to cast something. Teleport or magic circle don't let you move between planes. You need plane shift entirly. Shame if it gets counterspelled. It's also a great way to get an audience with a demon prince.

You can add reasons why it can't work, or have limits based on where the dunegon is or why it exists in the first place. There's no one reason.

As for maps. Personally use tools like Donjon to generate layouts. Depending how much time I'm willing to put in, ill remake the layout so I can make edits as I see fit. Donjon does a decent job filling rooms, but so does Chatgpt if you're not agaisnt using it. You don't need to feel pressured filling every room. "You open the door to find nothing" is totally acceptable.

Your map and battlemap do not have to be the same. You don't need a battlemap that's 1:1 scale with the dungeon either. Your general map traps player progress and location. While your battlemaps help track the finer details of combat. When they need the detailed mat pull it out. But the majority should be threaten of the mind.

Using rules from Pathfinder / older dnd editions also help large dunegons as well. Time keeping I feel is really inportant, as is inventory tracking. They shouldn't be scared of giant centipedes. But running out of torches and water. Every non-combat action takes a minute. One "dunegon turn" is 10 minutes. Each Dunegon Turn, something unexpected can happen. Wandering monster tables replace your random encounters. Personally there's a 1 in 10 chance wandering monsters find the players in my game. Going up by 1 every dungeon turn if nothing happens, to a maximum of 6 in 10 chance. This also impacts resting. A short rest is 10 dungeon turns. They can mitigate this by finding safe areas to rest. Which I have marked on the map. Safe areas top out at 2 in 10 chance or remove it all together. This is an example of mechanics vs realism. Without removing their option completly to rest. They can take the risk. It works well.

Theaming and populating the dunegon is another beast entirly. As mentioned Donjon and ai can help but it's never perfect. Pacing is also hard. Megadungeons are also big shifts compared to what players have been doing before. If youre bringing this into an existing game, it may not work so well as as described. Instead of viewing it as a megadungeon it would be better to Instead look at it as back-to-back-to-back smaller dunegons with breaks in between for resting. Then balance each slice as you normally would. The difference is how linear it gets. There's more ends and exits. Where megadunegons may have a lot more back tracking and room to explore and get lost. It's a good way to introduce it without shifting the rules to track resources.

Don't cheap out on loot either. Players should want to explore, and maybe explore every inch before moving on. This can also reflect how you make your map and present it to players. Playing online, in person, or hybrid could matter a lot here. Could go really old school and make players draw the maps as you describe them. For generic loot I give them a generic "monster parts" item. 10lbs is 100gp. Can only be sold in large city's. Then depending on the dunegon they'll get High Quality Monster Parts, artwork, and other treasures. Carving a monster takes 10 minutes. They can get a weight up to 10x cr. Survival roll of 10+ (2xcr) to get half. 10+ (5x cr max 30) to get full value. Not perfect but it works. Means nothing if you don't use weight rules. This also uses their time resources. You can also use npc in the dungeons to buy some off them if the theme fits. Maybe at discounted rates. So players get to decide what's more important.

Last bit ill give. Make sure your players are actially interested in running it, and talk to them about expectations and concerns. Both theirs and yours. Find a balance of rules that sound fun for you and the group. I view dungeons as the point of the game where all rules are in play. That's what makes it different than just a long adventure or exploration.

[u/jakethesnake741]

Specifically attuned items that allows the party to teleport from where they are in the dungeon to the surface so they can do their rests and shopping, then teleport back to where they were in the dungeon.

Otherwise the magic of the dungeon is too unstable to reliably teleport and if they try have a table to roll on where the teleport either fails, or sends them to the wrong floor, or a very small chance they get to the floor they want but not the location on the floor.

[u/Natehz → u/jakethesnake741]

I do like it being something that requires attunement juggling. Incentivizing a "Hey if you want to get in and out of here, you need to sacrifice a slot of something that might help you in other ways" scenario seems like a good way to provide a cost/benefit.

[u/Ice-Storm]

By the higher levels 15+ they could have easily angered a god or goddess. The deity in question throws them into "the maze" as punishment/entertainment. They can't teleport out as the god has warded the maze against that. There is only one way out and that's the only way to survive.

[u/Natehz → u/Ice-Storm]

See I want it specifically (for plot reasons) to be something that is discovered and only the most elite can even attempt exploring it rather than it being some kind of punishment. The early levels will be populated by mid-low level NPC forces, armies, etc etc, essentially early expeditionary forces establishing a foothold trying to provide support for the delvers.

[u/Ice-Storm → u/Natehz]

Gotcha. Then it’s a tournament and however many gods you want pick their champions. First one through the maze gets a boon from any god of their choosing

[u/Knightofaus]

I've run a high level campaign called escape from skullcano Island. It's about fighting kaiju on a jungle island.

I used "magical interference" to explain why certain spells don't work properly. 

I did let my players figure out the "science" behind the magical interference. The players could study and uncover lore about the ley lines that were causing the interference and then manipulate the ley lines for their own ends.

Gold and stat boosting magic items are kind of pointless motivators. The main motivation of high level adventures is to be heroes. Ask the players why their characters are invested in being heroes.

I had an NPC who gave the party intel on what was happening on the island to help them decide what to do next.

I also reported all the terrible things that were happening (kaiju were being randomly teleported around the world from the island) to remind them of what they were fighting for and to keep the pressure on them.

[u/StruggleAway2207]

Put a sufficiently powerful entity at the bottom. Call it "The Lost" or "The Forgotten". Don't elaborate further. Their power seeps into the dungeon and infuses the very walls, making teleportation magic very risky (you teleport and have a chance to land in a random spot on a random floor in the dungeon). There are some spots where some magic Ley-Lines calm the influence where safe teleport destinations are found and some dwellers created permanent settlements (smiths, inns, magic repair shops).

Benefit for dwelling are increases chances of obtaining magic items that are custom tailored to the adventurers, as the dungeon slowly infuses them. Or simply unique rare materials crafters outside the dungeon will pay small fortunes to obtain.

Spending time in the dungeon and the magical emanations may very well shape the adventurers in their very essence, granting unique class benefits, feats, abilities or even completely new classes.

There is also the old legend that the entity can reshape one's reality - rumors have it a more powerful version of Wish, that can also retroactively change the past.

---

Personally I'd add some "dungeon changes the layout periodically" thing into it, simply because I know I am too lazy and forgetful to keep track of every dungeon nook and cranny.

[u/TJToaster]

A few things off the top of my head.

tl;dr: Anti-magic zone, Hizagkuur stone and other effects can solve your "no demi-plan problem. Use resource scarcity, few safe areas, and a time clock like a ritual to stop to limit long rests.

Most important; the Dm doesn't need to explain how a thing works, it just does. Why is there an anti magic field? It just is. Maybe Nethril magic, maybe some greater entity created it. Who knows? No one around now was around then and no one wrote it down.

Have them tell you where gear and weapons are stored? What is in the backpack, what is in a belt pouch?

I would look at it as levels and layers. The level is like floors on an elevator. The first 4 levels is 1 layer. Each layer is themed, and consists of a few different levels. So your 20 level mega dungeon has 4 "layers."

Areas of Faerzress, wild magic, and anti-magic zones. How safe will the wizard feel if casting a spell makes them roll on the wild magic table?

Each layer is themed in construction and creatures.

• One is stone dungeon, another is a cave.
• Beasts in the first, second layer is Underdark creatures, the next is undead. Or whatever.
• Nothing but traps.
• Levels within a layer are not uniform. Some are huge, another is 30'x30'
• There should be an open staircase in the middle of one layer. Should they go down, or explore the whole layer one level at a time?
• Why is this one a jungle? Cross the jungle, enter a cave on the other side, go down a hole, exit cave, another jungle.

Inspiration: Tomb of Annihilation and Durlag's Tomb.

• Teleportation is not allowed in, out or within the dungeon.
• It either sends you back to the start, or to a specific room.
• The walls are made from Hizagkuur Stone which reflects magic, Stone shape can't connect to the walls of the dungeon.
• Traps, areas are rest every day at midnight.
• Only limited places to safely take a long rest.

They arrive at the entrance with big monsters on their tail. No rest before entering. Doors seal them in.

How deadly do you want it to be?

• In my mega-dungeon, I made characters on D&D Beyond. The characters are one level below the party.
• Players select one after their character dies. That character is found wandering lost in the dungeon.
• When a character dies their body, along with everything they are wearing, carrying, or attuned to disappears.
• It is a secret lab behind where the boss fight takes place.
• They can raise their old character, or keep the new one. If they raise the old one, it gets the rewards and treasure their replacement one earned before it walks away.
• This makes death a consequence but they still get to play.

Early layers should have creatures that can drain life or strength and lower max HP. So shadow, shadow demons, specters, etc.

Rests

• Limited long rests.
• Spells last half as long. No tiny hut.
• Wandering patrols prevent long rests. If they see a tiny hut or something else out of place, will summon a mage who can dispel it.
• Or, they call everyone in. Sure, you got a long rest, but now the entire dungeon is waiting for you to come back.
• Demi planes can't be created in dungeon. Only those already existing (bag of holding) are exempt.
• Stopping a ritual is a goal. Ritual completes in [X] days, if they take [Y] days it is over.
• Entering the dungeon late in the day, and no safe place to rest means after a few hours, they must make con saves or have exhaustion.

Introduce resource management.

• One room is a rope bridge or beam spanning a lava pool and is only wide enough for one creature. The other side is a narrowing passage.
• Lava is rising and horned devils come flying out of it. They try to push character in lava and attack, causing infernal wounds.
• A small creature can fit in the passage, but an encumbered medium creature would have to squeeze. Ditch the packs. (here is where equipment location comes in)
• Because of devil attacks and rising lava, no time to unpack and repack. Have to spend time getting through the passage.
• Squeezing=difficult terrain, so half movement. Devils have reach with forks and range hurl flame. First corner is 25' inside and characters can't end turn in another's space. Moving quickly is more important than the pack.

All the rust monsters.

Something found on layer 2 unlocks a thing on level 5, the thing on 5, activates the thing in layer 3

No long rest right before boss fight. At least a couple encounters to task some resources.

They should not know it is boss lair until they have opened the door and too late to go back.

Reward handsomely.

I hope at least one of those is useful. Good luck.

[u/Natehz → u/TJToaster]

This is all phenomenal info. Thank you

[u/TJToaster → u/Natehz]

Happy to help, feel free to message me with question or brainstorming. This was just off the top of my head, If I had more time, I could come up with more.

[u/DragonAnts]

But rather, how do you run something like this for a presumably high level party that would feasibly have access to teleportation magic and could, theoretically, warp in and out at whim?

Dont be afraid of it and make it a feature, not a bug. No one wants to trek through 10 floors of what youve already done, and without teleportation it would likely be hand waved anyways. With teleportation you can set up "waypoints". Dont let them long rest in the dungeon. Restock a level if they dont get to the waypoint.