My first mega dungeon was drawn out over... 6 newspaper sized sheets when i was about 11 years old and playing Rules Cyclopedia D&D. I don't think I ever ran it, though I did spend a fair amount of time stocking it! It was probably one of the most random assortment of monsters ever put to paper. As much as I enjoyed doing it, I was always dissatisfied with it, though at the time I didn't know why.
It was almost a decade later when I returned to a mega dungeon. This time it was Undermountan and my adventuring party only dipped their toes into the vast halls. This was the last time I ever messed around with a megadungeon, and I haven't really missed it.
Minidungeons (a word I first heard over at taichara's blog) were much more my style, even if I didn't have a snazzy word for them. They just made more sense to me than the huge sprawling complexes with everything plus the kitchen sink (mimic) thrown in. How would that work?!? Why are there gnolls next to a necromancer, next to a goblin clan, next to human bandits? And why are there human bandits so deep in the dungeon? Who are they raiding anyway?
For the past couple of months the idea of a giant dungeon complex keeps poking itself into my consciousness. Sending a group down into it's depths, not to see the light of the sun for weeks or even months... But how to make it work? How do you make a megadungeon make sense?
The answer I arrived at is this - A megadungeon isn't just a big dungeon, it's a huge one, sprawling over vast amounts of space. Sprawling is the key. A megadungeon is nothing but a series of interconnected minidungeons! There will be miles of tunnels with little to nothing in them, areas that started to be excavated but were abandoned before they got more than a room or two deep, lots of areas that would qualify as a minidungeon, and a few larger complexes that would take up a page or 3 of graph paper.
Why? Easy, why build something if there aren't any resources nearby? Areas that are dug out are dug out for a reason, and that reason usually will have to do with resources; water, minerals, lay lines, etc. and whatever resource is nearby will influence the construction of the surrounding complex. Exits to the surface or to lower levels, or areas where multiple sections naturally come together will be busier and have more variety of encounters. Areas without any resources will be empty. Why are there lots of long tunnels connecting all these mini dungeons? Well, there are lots of large burrowing creatures out there, and lots of natural caves, and people want to get from place to place in order to exchange things... plus with thousands to millions of years of underground empires, it's logical to presume that various avenues would have been created.
So where will my megadungeon start? At the top! More to come...