|In a case of nominative determinism, this piece is by "Chase Stone"
Beloved one-page dungeon the Skyblind Spire includes a brief piece of lore-- the impossible architecture of the tower and the magic it generates is the result of "Kastromancy," apparently a discipline for discerning how to use strange layouts to create potent magical effects. This is an elegant inversion of the usual admonition of the "funhouse dungeon", which is that if the contents are fantastical, you shouldn't expect them to be laid out in a reasonable way.
Kastromancy can be extended to be more useful to gameplay. If a structure is applied to the foundation of the art, it can be employed by high-level magician PCs to build their own dungeon spaces, to understand dungeon master rivals, and to create valuable resources to seek out, destroy, refine, create, and treasure.
Domain-level play through the establishment of keeps, construction of trade guilds, and nourishment of congregations is helped along by the basis normality of such things. They are real things, with countless examples in the real world. Domain-level magic, and magical projects generally, lack a real-world analogue. If a magical problem lacks a mundane solution, the magical solutions a player thinks of is only as good as the fictional magical framework established in the setting.
The two rudiments of kastromancy are physical room layout and kastromantic arrays, and they must work in tandem. Anything weird or "unrealistic" about dungeon layouts are a result of kastromantic principles-- octagonal rooms, gridism, 10-foot-wide doors. Most kastromancers find it easiest to arrange their lairs underground or in tall towers, where the base functions as a magical nexus. Students of the Convenient Art use random architecture oracles to discover new principles.
Kastromantic arrays are made of certain magically-resonant stones. Their type determines their general effect, while occlusions or details affects their expression and their cut affects how they can fit together in an array. A kastromancer may rejoice to find a heart-cut clouded fire opal, since it just fits so well with their tear-drop pure emerald in the strict mathematical edicts of their array diagrams.
A dungeon that has been sufficiently cleared out to be made safe can be thoroughly searched by a magician to sniff out where the array is held, buried at a central location or hidden in a clever chamber. It might have 1d4 stones for each level, plus one for each weird magical effect in the dungeon that must have come from kastromancy. If you're reading an old module that explains how a fountain was filled with ever-flowing acid due to a wish spell, this is likely the module author dutifully concealing the Convenient Art from mortals. Kastromatic stones are found in the possession of dungeon masters, on the wizard black market, or sometimes in the possession of mining and jeweling enterprises. Wizards generally try to keep the existence of kastromancy from mine-rowdies and industrialists for this reason.
General Shard Types
- Divination. Might let a dungeon master know when trespassers arrive, let them look around with disembodied eyes, or project their spirit as a massive glowing head to yell at rival adventuring parties.
- teleportation/impossible geometry. See the link to the Skyblind Spire above.
- impossible weight-bearing. Build ever-down, minimizing support structures, and last for countless ages.
- Pacts. Summons monstrous humanoids of various sorts. A one-time calling, but prevents normal turnover. The magician reliably knows what kind of group they are calling, but not the specific group or how long it will take them to arrive. Does not assure loyalty or prevent coups.
- Anti-gravity. Also anti-friction and other physics tricks.
- Shrinking/growing, and its remedy. Some allow for more terrible transformations, such as the famous "Dying Breath to Dire Boa" transformation.
- Preservation, either a temporal stasis or a reprieve from age.
- Haunting, soul capture, and spookums.
- Boundary stones. Keeps monstrous denizens in their assigned rooms.
- Bullshit antimagic. "Teleportation effects in the dungeon instead teleport the user to the elemental plane of fire." "All attempts to charm the statue make the caster permanently insane." "Speak with dead now makes you shit yourself and bite your tongue at the same time."