Since I started the Traveller campaign (which will have its own blog in a day or two) I have, naturally, started planning other campaigns I might run in the future instead of working on it. In particular, I've started thinking seriously about running a megadungeon again. I've been going off and on the idea for a while now, particularly since Swords & Wizardry came out. Every time I read about a great megadungeon campaign on Sham's Grog 'n Blog or Grognardia or The Society of Torch, Pole, and Rope, I get really excited about running my own -- and then I get distracted and wander off to plan and run something else.
I haven't managed to get much done during the enthusiasm phase of these cycles, but a few things are starting to stick. No maps, no room descriptions, not even a general idea of what the levels are, just a few vague notions.
First, I'm thinking the first level or two is going to be the sewers/catacombs of a city. Non-sensical fantasy sewers, with goblins and bandits hiding out in them and little shrines to evil gods, but sewers the same. Below that, things start to get weird, but the first few levels are relatively normal, though they don't make good civic sense.
The trouble with this notion, and the thing that keeps me from embracing it wholeheartedly, is that it seems to suggest that I'd have the whole city above it mapped out in similar detail, which I'm not really up to doing. And if I did that, I'd start thinking about whether said sewer conformed to medieval standards, and then I'd be spending my time on wikipedia rather than working on the dungeon. I suspect I can solve my problems by going "pfsh, there are entrances where I want there to be entrances, and the PCs are never going to map out the dungeon and the city accurately enough to figure out whether they match up" and leave it at that.
And, as much as I like the idea of urban adventure, on any given day I'm just as likely to think it'd be better for the main home base to be some little village out in the middle of nowhere. Or at most a medium sized town, something more manageable than a city, since I'll already be spending a lot of time working out the dungeon proper.
The other major idea I've had is that the dungeon, or at least part of it, is not just an underworld in the usual dungeon-y, it is The Underworld, the realm of the dead. This makes a pretty decent explanation for why everything down there is so weird, in case my players start asking pesky questions, and would make for an interesting series of sub-levels. And it gives me an excuse to make the entrance to the dungeon or some of the doors within it great gaping stone demon maws, whose teeth you must walk under to enter it.
So. Now I've got that out of my head, and I can go work on my Traveller game.