Building the megadungeon: Establishing history and purpose

What the hell is that???

I put in some more work on the megadungeon, and I've changed my approach. 

I'm getting sketchier and looser as the dungeon progresses and that initial burst of enthusiasm wanes. Arguably I should have started out this way.

Rather than working in Adobe Illustrator and creating detailed, finalized levels from the get go, I've switched to sketching them out loosely in ProCreate. Actual planning! This allows me to revise them easily as ideas occur. I can also connect multiple layers together, whereas the more laborious method using Illustrator inclined me to work only one level at a time. It's low lift and I can revise levels as time goes by, and the campaign requires me to rethink the initial designs. 

Building a megadungeon is just too daunting to do all at once.

What else have I learned?

First, you need a loose outline of the dungeon's purpose and history. This greatly helps guide layer design. Without it, it becomes random and senseless. The history of Druidun is long and convoluted, primarily in order to justify a varied environment, but yours doesn't need to be. 

All you need is a logic guiding the initial layout. After that, adjust with subsequent inhabitants and what they might have done to the original structure. Goblins, for example, might dig tunnels to connect rooms, or to follow a streak of ore, or create narrower tunnels that keep out large predators from their dens.

"Listen, Princess, I'm in it for the loot."

So what's the history for Druidun? 

The upper levels were originally dug by druids, to commune with the roots of the earth, and for their tombs. The druids expanded it to be used as a refuge during the Undeath Plagues, like Derinkuyu in Turkey, with rolling stone slab doors, extensive living quarters and even areas for animals. 

I also decided that the druids were drawn to the area by the conjunction of Ley Lines, and the powerful magical energies that existed deep beneath the surface. These energies were created by the Titans, who conducted the first experiments in necromancy in their underground laboratories and zoos, safely sealed beneath the earth. 

Later, a castle was built atop the druid ruins, and it became a stronghold for the Mercian Kings. They wanted to establish control over the magical energies below, which were studied by their wizards. They would be crowned here, to imbue their reign with mystical energy.

The wizards discovered that the intense magical energies had drawn Xorn to the area, long ago, and the hulks of dead Xorn made the earth rich in all manner of minerals; it also created magical ores thanks to the conjunction of multiple realities. This was of intense interest to the dwarves, who were brought in by the human kings to mine the earth and build a panopticon prison to house rebels and malcontents of the Mercian regime. These poor souls were also subjected to magical experimentation.

The dwarves called the site Karak-Thun, and it became fabulously wealthy. Eventually, they dug too deep, breaking into the Underdark. Powerful magical energies, chaos leeching in from beyond, had imbued the creatures in the area with great size and power, and mutated others. The dwarves were driven back by a flood of giant spiders and other horrors. A war went on for centuries, until finally the dwarven colony collapsed, the survivors fled, and the wealth was abandoned to chaos. 

More recently, a rogue order of wizards moved in to conduct magical experiments, and they opened up an energy nexus to other planes; eventually they were shut down by the Thaumaturgical Order. But the nexus remains open, and it's pumping into this reality powerful magic, resulting in an outbreak of the undead.

That's a brief overview. There's more, although arguably there shouldn't be. It's just meant to provide me with a number of threads to pursue when designing levels. 

You only need a high level background. Mine is probably too complex and convoluted, but it allows lots of variety. 

"Yes, it may be the Pool of Infinite Evil, but that doesn't mean it isn't drinkable."