In the most recent Questing Beast Q&A he and his guests gave their thoughts of "ideal dungeon size" and it got me thinking. Here's a link to the part of the video where they discuss it. After some consideration, I want to propose 4 basic size classes of dungeon, divided partially by number of rooms but, more importantly, by the effect they have on the core gameplay loop of your campaign.
These are your 5-Room Dungeons, your Delian Tombs, your DCC funnels, etc. Pretty much anything between 1 and 6 or 7 rooms. The 5E starter kit has one as its introductory dungeon immediately after the combat encounter that kicks off the campaign, and it's pretty damn solid. By definition, you can pretty much always finish these dungeons within a single session. That makes them ideal for one-shots, and indeed, they're popular at conventions and instances where you're introducing new players into the hobby.
But if you're playing a whole campaign, I think they can serve a special role that's underappreciated. For one thing, collecting tons and tons of tiny dungeons is a great thing to populate an open world sandbox map. You just sprinkle them in everywhere and boom, you have a whole "land of adventure!" There's something really cool about how Breath of the Wild broke from the Zelda tradition and switched to having dozens and dozens of tiny shrines dotting the map instead of 6-10 medium-sized dungeons. This is also (sorta) the idea behind Barrowmaze, which is a really cool adventure that does the same concept.
My sessions are averaging around 5 hours at this point. A medium sized dungeon usually takes us 2 or 3 sessions to play through. But a micro dungeon takes us 1 or less. In fact, we've had sessions where we complete 2-3 micro dungeons all before the end of the night. And I mean the full cycle. Get the quest in town, do some research and prep, travel to the dungeon, clear it out, haul the treasure back to town, rinse and repeat, multiple times in one session. It feels unbelievably cool to do that. Obviously you can point out that micro dungeons have less creative potential than medium dungeons and are going to be a bit shallow (they especially can't do anything fancy with layout and Jaquaysing techniques and whatnot) but the tradeoff is an incredible sense of accomplishment after the session is over.
"We just did 3 quests in one night! Holy shit!" Even if it's the same total amount of content overall, it feels more satisfying in a way.
So yeah, I actually think micro dungeons are really good for when you want your campaign to be focused on dungeoncrawling as the main activity. Either your players are operating out of one hub town and they're slowly clearing out the dozens of shrines in the surrounding wilderness, gradually cleaning out the whole local region, or you have your players on the move throughout the kingdom and just doing tons of shrines along the way.
You can also easily make a procedural generation system for this kind of campaign. I use 24-mile hexes for my large scale and 3-mile hexes for my small scale. So you could have a procedure that says "every 24 mile hex has 1d4+1 micro dungeons in it." When the party enters, you roll 1d4+1 and then place each dungeon into its own 3 mile hex within the 24 mile area, then put one rumor for each dungeon in the main settlement of that 24 mile area.
These are the majority of all dungeons that get designed. Most of the ones in The Lost Mines of Phandelver and other 5E books, the Sunless Citadel, Tomb of the Serpent Kings, Tomb of Black Sand, the Waking of Willowby Hall, most Dyson Logos dungeons, Hole in the Oak, I could go on and on. Unintuitively, most 1-page dungeons would actually be in this category, just because people are getting really good at packing lots of content into a small space.
How do you make good medium dungeons? What can you do with a medium dungeon? What are they good for? Well, to be honest, most advice people give on designing dungeons just assumes this size by default, so go ahead and apply most of what you know about dungeons to these ones. Try to make each room cool, have some variety, use interesting layout, maybe some competing monsters, a few secrets here and there, etc.
What I tend to find that medium dungeons are really good for, as weird as it may seem, is campaigns that don't focus on dungeoncrawling. Or rather, ones that only occasionally have dungeons. If you want a campaign that's close to 100% dungeoncrawling, then I think the other options on this list are better, but if you want about 1/4 or 1/5 of your sessions to be spent in dungeons then you should make them this size.
Like, the 5E campaign I've been a player in for the last few years I would say has had about 1/5th of its sessions be dungeoncrawls. Another 1/5 might be wilderness travel, another 1/5 is spent in settlements (talking to NPCs, investigating, shopping, etc.), and another 1/5 is just boss fights. Since high-level 5E has really long combats and it's very much an action game, we rarely have combats that aren't bosses. If the fight is gunna take us hours to do, then we might as well have something fucking awesome and complicated to deal with, and luckily my DM is really good at designing 5E combat scenarios that can keep you interested and thinking about your choices for 5 hours straight. It's just that you definitely wouldn't want that kind of thing more than 1/5th of the time. The last 1/5 I would say is just "miscellaneous" stuff, especially goofy roleplay sessions.
So if your dungeons are medium sized then you get about 2 or 3 sessions out of each one, and that feels like a good amount of dungeon if you know that it'll only be comprising a fraction of the total time. A megadungeon would be wasted if you only spend 1/5th of your time engaging in it and a micro dungeon would feel like a really insubstantial session when you had other adventures that were, like, 2-3 session-long arcs about mystery or travel.
Megadungeons, in two types
Megadungeons are just defined as "unusually large dungeons," but over time there's arisen some traditions and best practices in megadungeon design. If you've ever played a Metroidvania (Metroid, Castlevania, Hollow Knight, the first Dark Souls, etc.) then you can picture a megadungeon. It's so large that it's usually split up into regions that could each be their own medium-sized dungeon. This is your Rappan Athuk, Maze of the Blue Medusa, Caves of Chaos, Undermountain, Dead in Thay, etc. And megadungeons are absolutely optimized for dungeon-focused campaigns, because they offer so much to keep discovering. It would be a waste of a good megadungeon to only visit once or twice and then move on to other stuff.
Thing is, megadungeons were actually the default back when the hobby was created. In the Original D&D booklets, in the section where they define dungeons and how to design one, this is what they say [emphasis mine]:
In beginning a dungeon it is advisable to construct at least three levels at once, noting where stairs, trap doors (and chimneys) and slanting passages come out on lower levels, as well as the mouths of chutes and teleportation terminals. In doing the lowest level of such a set it is also necessary to leave space for the various methods of egress to still lower levels. A good dungeon will have no less than a dozen levels down, with offshoot levels in addition, and new levels under construction so that players will never grow tired of it. There is no real limit to the number of levels, nor is there any restriction on their size (other than the size of graph paper available). “Greyhawk Castle,” for example, has over a dozen levels in succession downwards, more than that number branching from these, and not less than two new levels under construction at any given time.
A dozen levels?? And this is the example drawing they offer:
This is the more traditional kind and the one I bet most people reading this are thinking of. These megadungeons are still constructed as though they're one building. There may or may not be hallways between rooms, just as with all dungeons, but even if there are I bet they aren't super long. It may be a truly stupid number of rooms, like dozens or even hundreds of rooms, but overall they span an area that's still no bigger than, like, an airport or a school or something. For example, here's the layout of the Maze of the Blue Medusa:
So rather than having one big dangerous castle or tower or something, you have pockets of dungeon living beneath the surface spread throughout a region. Here's an example diagram of a sparse megadungeon (imagine it as a cross section):
So you have a city on the right, a mountain on the left, and some farmland in between. But underneath all of that is a series of dungeons that are all interconnected. In this way, it feels a bit more accurate to refer to the dungeon as "the Underworld" since it's literally just a layer directly beneath our world.
You can also see that I've marked which areas are under control of which factions to start out. Three large ones and one small one is pretty good. So wherever the players enter the dungeon from, they aren't just going to clear out that space and haul in all the riches. They'll be facing one piece of a larger network of allied forces. And while they could totally wipe their enemies out, they'll just as likely force a retreat to some other area. Plus, the factions are scheming against each other to expand their own territory in key areas, so the makeup of the megadungeon will change even without the players' involvement. Let's take a look at how this dungeon might transform after you throw some PCs at it.
So if we return to the idea of the procedurally-generated dungeons as previously discussed, then imagine this: every 24 mile hex has 1d4+1 dungeon areas, but they're all connected across the region. When you zoom in to the 3 mile hex scale, you start sprinkling their entrances in the Overworld throughout the 24 mile area. The hub town, the forest, the swamp, the lake, and the ravine all have their own dungeons underneath them that are all part of a greater network.
I also like this scale because you can have a "room" of the dungeon be, like, a whole cliff face that needs to be climbed. Or an entire chasm in the earth. Or, I dunno, like a lake. And you can put things like Underworld settlements in as part of the megadungeon. A whole-ass goblin town is just part of the network as one of the regions. Or something nice and chunky like an arena.
Also, as I've ragged on about on this blog before, the standard assumption of "120 feet per 10 minute turn" is beyond absurd. You don't need to read this whole post if you don't want to (it's actually quite out of date) but if you skip to "Big Difference Number 1: Movement" then you can see me put this one to death. There is no combination of excuses or reasonings that can ever possibly justify such an insanely slow pace, even if you go with the interpretation that "it assumes players are being thorough and careful." It's actually difficult to travel at such a slow pace, like, physically. Try it. Try stretching a 120' walk out to 10 whole fucking minutes.
So instead, if you go with a reasonable pace (the most realistic being 3000 feet per 10 minutes but I'll accept something lower), then having a really wide dungeon helps you get more out of that. If you're walking from the sewers to the burrows to the gold mine then maybe it'll take you a few hours at a pace of 300ft/minute. If you did 12ft/minute it could take you days.
I don't really have any way to wrap this up. It was just something I was thinking about and I thought maybe others would find it interesting. Obviously the line between each broad size category is pretty blurry but I do find it interesting how important it can be in defining the entire dungeon experience.