The shelters (Prismatic Planet)

The Fallout setting has the best rationale for wacky dungeons being scattered all around. Each "vault" was designed with a unique, often disturbing social experiment. This means every underground facility can have wildly different themes: psychological horror, body horror, mutated monsters, utopian simulations, illusions, traps, advanced technology, and so on.

Here are a few examples compiled by A.I.:

Vault 11: Residents had to sacrifice one person annually or face annihilation.
Vault 108: Filled with clones of a man named Gary. All they say is “Gary.”
Vault 12: Deliberately left unsealed to expose residents to radiation—birthplace of ghouls.
Vault 22: Botany experiment gone wrong—plants infected and consumed the inhabitants.
Vault 75: Children were taken for genetic enhancement; adults were exterminated.
Vault 81: Secret medical experiments conducted behind a facade of normalcy.
Vault 95: Rehab center for addicts—later flooded with drugs to test relapse.
Vault-Tec University: Training ground for Vault Overseers, filled with simulation chambers.

Here are other examples.

I find this much more satisfying than "crazy wizard did it because he is crazy" of some D&D modules.

My Prismatic Planet setting has something similar, with a few twists of my own.

---

Most Prismatic Planet "dungeons" were created by the progenitors. These are inhuman creatures that view humans as little better than common beasts. Before being driven to the brink of extinction, they not only enslaved humans but also ran various twisted experiments on them to test their physical, mental, and moral limits.

[Other dungeons are created primarily by gigantic prismatic worms and later repurposed by humans or other beasts]

The progenitors knew they were a dying breed even before the scorching of the planet, so they used the much more numerous and expendable humans for various tasks.

This means that their "shelters" often contained actual labyrinths, tricks, and traps to test or even mutate humans in various ways, treating them like lab rats. Some of them might have included small prizes to encourage people to complete random tasks, while others were deathtraps designed to cull the herd and leave only the most apt humans for breeding purposes.

Each trap can contain information of various bygone ages, humans (different, crazy, or unharmed) and even surviving progenitors. Some are found intact, while other have been invaded, robbed, or overtaken by monsters or bandits.

They can also work as a great campaign starter, similarly to a Fallout game: the shelter is all the PCs ever know, until the systems stop functioning for unknown reasons, forcing them to venture out into the wider world.

It would probably be a good idea to list a few examples in the book. Here are a few of my own. I think I can also use some from Dark Fantasy Places.

1d6.

1. Controlled by an AI with an [helpful, hostile, erratic, suffocating, jealous, mischievous, dishonest, bargaining] personality.

2. Clone factory, has several humans with little to no memories or understanding and [helpless, aggressive, childish, curious, submissive, rebel] personality, or preserved in cryogenic chambers.

3. Mutation lab, including mutated humans, beasts or plants of various kinds.

4. Arena, created for entertainment and selection purposes, with various systems prepared to pit humans against [each other, robots, clones, beasts]. 

5. Mazes, sometimes resembling escape rooms, created to test the subject's [intelligence, morality, courage, resistance].

6. Experimental science labs, dedicated to the research and improvement of [weaponry, armor, transportation, communication, medicine, psychotropics, psychic powers, robots].

---
Back to the table of contents.

As always, all feedback is appreciated!