As I worked on the bits and pieces of my pulp fantasy campaign setting, I realized that I needed a megadungeon of my own. I used to be somewhat contemptuous of the notion that old school fantasy gaming required such a thing, but I've slowly come round to the belief that I was wrong to be so dismissive. I still believe that a campaign that revolves entirely around a single megadungeon is probably going to be too narrowly focused for my idiosyncratic tastes. Yet, I also believe that a megadungeon is an important component in establishing the proper vibe of old school play. Neither Greyhawk nor Blackmoor was solely about delving into the dungeons beneath their eponymous castles, but it's hard to imagine either campaign without the megadungeons from which they derived.
Thus was born Dwimmermount. Once I accepted that I needed a megadungeon, I knew I needed a proper megadungeon, which is to say, one that was a suitable potpourri of danger, discovery, and whimsy. To achieve the right mix, I came up with the idea of a mountain that set atop a node of primal Chaos. When the Eld invaded, the mountain called to them and they responded by establishing a fortress there to plumb the mountain's depths and harness the raw Chaos that seemed to roil up from beneath its roots. Over the centuries they occupied it, the Eld mined deep into the mountain -- and beneath it -- in the process creating many chambers and expanding the natural cave systems of the place.
Later, after the Thulians overthrew the Red Elves, they occupied the fortress, dubbing it Dwimmermount, a pidgin word incorporating the Eldritch word "dwimmer," meaning both "magic" and "chaos." The Thulians continued the work of the Eld, adding to the vast complex within and beneath the mountain, gaining deep insights into the workings of magic -- and being slowly driven mad by the raw Chaos that permeated the place. Some of the Thulians and the servants, like the Eld before them, were forever changed by spending so much time in Dwimmermount, leading them to delve into things that only accelerated these changes, to the detriment of all.
Like the Eld before them, the Thulians fell to their own hubris and Dwimmermount was shunned by most civilized men, who rightly saw it as a lair of madness and corruption. Yet, there are some who brave its dangers nonetheless, seeking out the magic of the Eld and Thulians alike, as well as the treasures they dredged up from the depths. Few who do so who return and fewer still return with their minds and bodies intact.
That's the rough sketch of the thing. The idea is that Dwimmermount isn't an entirely natural place, so I have an excuse for lots of weirdness when I need it. Likewise, it's not completely artificial either. One of the problems I always had with many old school megadungeons is that they're supposed to have been built by some mad wizard or other, but they always came across as simply too loony even for that explanation to work. And because there were (at least) two different groups, with slightly different agendas, who occupied Dwimmermount over the centuries, I have some leeway in varying the look, feel, and contents of the levels and chambers. In short, Dwimmermount is meant to give the illusion of naturalism to what will be a semi-funhouse dungeon (but only semi; I have my limits).
More on this as it gets developed.