"listen kid. When it comes to dealing with a dungeon, there is never a moment of being too careful, there is only you not being careful enough".
There is no one that knows, or can come out in public and boastfully admit to knowing how a dungeon fully operates or the exact process it goes through before finally becoming a dungeon.
The only thing they know of, is that dungeons are mostly formed in a land corrupted by mana, and what determines their level, is how high the land is corrupted by the mana; that is all.
Why is mana the thing that brings about the form of a dungeon? No one knows. Or how there are some monsters in a dungeon that no matter how many of them is killed, when one comes back the second day, the dungeon is still filled with the same monster types that were killed yesterday? No one knows.
Dungeons have been considered a force of nature, and like any other force of nature, they work in ways that one can only assume on, not be assured of.