Why are there so many zombies and skeletons in the dungeons?
Most dungeons are partly tombs, crypts, mausoleums, hypogaea, and partly ruins of ancient cities or fortifications, and what is a lost city if not a large cemetery?
But the dead don’t come back to life in any cemetery. What do dungeons have that make them prone to this inconsistency of the natural laws of life and death?
Magick-Users, of course
Magick-Users play with “forces” or “energies”, “agencies” or “intelligences” that seem to defy the natural laws of the universe or, at least, human understanding of those laws. We call this discrepancy Chaos, because we can’t see the order or the laws that govern it.
Magick-Users (and Clerics as well) are repositories of such forces (or energies, or agencies, or intelligences… let’s call them “forces”, then, or magick), that is, spells.
(Magick-Users are more or less aware of how they channel magick, manipulating weird forces at will. Clerics are not aware of the same; they believe that their gods grant them their powers, they don’t realize that their prayers are magick formulas, identical [in latent if not in manifest content] to the Magick-Users’ formulas, and that through them, they “steal” their powers from the gods, who are not really gods.)
The frequent observation and praxis of magick transforms the world around it. Over time, the places that were once centres of study or use of magick, such as laboratories, temples, towers of stargazers, fairy rings, necropoleis, akelarres, begin to present anomalies.
This is normal now
One of these anomalies is the disruption of normal, ordered life and death cycles. The dead in the area begin to return to life (or to a parody of life) and roam the place. Probably hungry and angry, and totally baffled.
Another is the appearance of the weird, including monsters and traps. Raw magick sneaks through cracks and recesses accidentally opened by the practice of magick. Unchecked magick has the tendency to produce unexpected effects, such as the opening of gates to parallel, adjacent or perpendicular worlds (or universes?), and these gates are crossed by their inhabitants.
Sometimes, finally, the reality on the other side pollutes ours. That’s why there are rooms with inverted gravity, or full of water, or where magick does not work properly, or of impenetrable darkness, or any other imaginable or unimaginable effect.
But we were talking about the undead.
Another kinds of undead, such as vampires and ghouls, less instinctual and more rational (so to speak) than zombies and calacas, could simply feel more comfortable in an environment with residual magic, for them it’s like going to the beach*. This is why ghosts are so happy in houses where misfortunes and tragedies have occurred.
*I hate going to the beach; if god** wanted us to go to the beach, he would have made us crabs.
**There is no god.