Mages can study dungeon-making at school, though the subject is apparently quite difficult.
Dungeons always have a connection to the outside world or else the flow of magical energy will be cut off. Magical energy is sparse at the entrance of a dungeon. Spells appear to be stronger than normal when cast in a dungeon.
There are several stages of dungeon maturity, according to the Arcane Crusaders:
Level 1: the dungeon is discovered.
Level 2: something valuable is found, resulting in an increase in the number of researchers and adventurers in the area, bringing trade and prosperity to nearby towns.
Level 3: the dungeon is explored to deeper levels and the profit made on upper levels decreases, with skilled adventurers heading deeper to make a living and a decrease in the number of new adventurers.
Level 4: the inner layout of the dungeon changes, with stronger monsters appearing and valuable items once again being found on upper levels. This is the point at which the Arcane Crusaders wish to stop the growth of the dungeon.
Level 5: the monsters become too numerous to destroy and spill out onto the surface, causing mass destruction.