So, in returning to my megadungeon idea from the original City States game I realized there were three reasonable places to put it. Each is unique and in my inspiration has what is required. I thought I faced a tough choice.
Or do I?
If the megadungeon is a mythic underworld does it have to be in a single location. We’re not talking multiple entrances like most have, but multiple locations such that it can be entered in places as separated in our world as America’s Stonehenge, The Seattle Underground, and Carlsbad Caverns (which while not my goal here, if I wanted a megadungeon for my Demon Haunted World this would work).
Nor I am talking about something like the Underdark in the Forgotten Realms. There would be no realistic sense of distance or magical gates that connected the sections. You could simply walk through a normal dungeon region and walk out thousands of miles away. The problem, of course, is how to justify this without making it a valid route of travel for people. If that was so the dungeon, or at least the trade routes, would be controlled by some power for that purpose. Although, as an idea, that alone isn’t too bad if used sparingly.