How There Are So Many Dungeons
In a prior post I answered why there are so many irrational dungeons. The big problem is the fact that it is so difficult to build underground. The labor pools required, even if managed, would preclude keeping the structures secret. Nor can fantasy dwarves account for all the dungeons. So it must be magic. But in what form?
This magic must be accessible to a single individual, and separate from whatever class or abilities they have. Even powerful mages would lack all the kinds of magic needed. This is beyond a specialty. So its form would be a magical item. A very powerful magical item. In D&D terms, a minor artifact. Manifesting from the mythic underworld.
It would create neat hallways, rooms, stairs, sturdy wooden doors, furniture, lighting, and all the other irrational structures of a traditional fantasy dungeon. No digging. No debris. No effort, really. Malleable reality, very localized.
Using the magical item would simply be a matter of pointing it. More of a wand than a tool. Something that belongs in a dungeon, though. Something that its wielder could set down at the end of an episode of insanity, and easily take up again at the beginning of the next. Also a disguise.
An iron torch carrier. Just put it into a wall sconce when not in use.
All it lacks is a name.
Addendum: a discussion of this blogpost reminded me of the Winchester House. This magical item would single-handedly enable such an irrational structure, just underground.