Continuing on from this post

We've got our ball and stick model with (mostly) thee lines per box.

Next, think about something worth building a dungeon over. The more potential you shove into this purpose, the more you'll be able to come back to this particular well when thinking of what's in the rooms.

For this one, my big idea was "mummy holding a Scrying orb".

I made a note of that for use in the rumor chart later and started making the A and B plot of the dungeon.

B Plot: I'm starting with the ancient plot, since that will give me some ideas for influencing the current one, and what the dungeon is all about. I'm going with "temple of snake goddesses". We'll just say the Scrying orb is some kind of religious artifact and the mummy is an interred high priestess. There's a million snake bad guys in this game, so I'm reasonably certain that I won't have any trouble grabbing baddies from the monster manual to fill it out.
A Plot: For the current plot, nothing like Arabian nights with a little hint of Cronenberg: desert bandits turning into snake-people. Also, I never get to use yaun-ti, they're perfect for this; different ratios of snake and person, really fun mix. We'll say that these were human bandits who found the temple and started using it for a hideout. Its magic is transforming them into yaun-ti, giving them the power to talk to snakes, that kind of thing.

Having just one faction in a dungeon isn't par for a decent dungeon. We need a rival faction. Going along with the snakey theme, I think a medusa in the lower levels would be a great bad guy to use. I'll give her a blind minotaur boyfriend to increase her threat and because its unusual and cool.

Making certain I hit that dungeon par, I've got to put a weird nonstandard trick, a multi-room puzzle, and some logical traps protecting ancient treasure. Lemme sketch those out real quick:
•   I'm going to steal the snake transformation from Dante's Inferno because I loved that bit. I'll link that to some magical sarcophagi and aaaaawaaayyy we gooooo!
•   A statue which needs stuff put in its hands is pretty classic. I'll put the stuff it needs on two different levels and lock the mummy and orb behind it to incentivize players to look for them (and thereby engage with most of the dungeon)
•   We'll fill that floor with traps too, play up the temple of doom angle a bit. That'll also make our floor 2 a nice buffer zone which explains why the medusa and the bandits haven't just eliminated each other in open combat yet.
•   You know what? I'll make it easier to get through that floor if you're a snake. That will encourage players to experiment.

So, before finalizing the blueprint, I want to know what the in-game and meta-game purpose of the rooms are, so I'm going to make the key. This lets me catch any elements which don't make sense, or don't encourage creativity, strategic thinking, and puzzle solving.

Once the key is done, typically I would hit the graph paper. In this case I'm using MS Paint for demonstration purposes. I just make a quick square grid and get painting. This is the lengthiest part of the design, but super important; actually seeing how the levels work in two dimension helps you to catch any inconsistencies which would make them not work in three dimensions.

Once the map is done, I shift back and forth a few times between the map and key until I get the dungeon feeling nice and challenging. At this point I make the wandering monster charts per floor, into which I put the behavior of the dungeon's denizens (I do this rather than more advanced techniques because it is easy and I am lazy)

Once I'm satisfied, I add a few details to make the dungeon fit into an ongoing campaign. I give it a rumor chart based on the elements in the dungeon, a triggered event for when players enter its hex, and I make the magic Scrying orb a little cooler than usual by giving it some character.

Now my dungeon is compleeeeeete! Not bad for an hour and a half's work.