They've cracked the code. Some facet of reality seems to work along platonic solids.

A dagger has 4 potentias, 4 possible phases, and can be represented thaumaturgically with a 3 sided pyramid. 1d4.

A fireball seems to reach its maximum in multiples of 6. d6s.

And so on.

But the key determiner of reality seems to be the stable point of phasic potentials- a 20 sided decision. If you were to rerun reality over and over again, it is this phasic array, represented runically as 1d20, is the most common variation of any luck-based event.

This is this universe's fibonacci sequence. Its pi. Its plank constant. The universe has fixed variations, fixed probabilities, a fixed quanity of potentia, of random.

And as such, it can be manipulated. It is known that some people live their lives according to the whims of fate, and somehow manage to manipulate the unmanipulateable. Charismatic rogues and certain spellcasting traditions caress the tender bosom of the universe and get rewarded with time rewriting itself- Fate is fickle, but it can be bribed, it can be tricked, it can be persuaded.

So. If it can be manipulated... What happens if you build a structure that represents it? Worshipping each facet of fate. The terrifying low rolls, the middlish mediums, and the much-lauded high? 20 places of worship, each connected, an edifice, no, a shrine, no, a glorification of all possible fates, praising constantly the concept, the domains, of luck and fate. Structure, ergo sum. You build a thing in its image, and the image is the thing.

The dungeon is fate. or luck. Or something close enough.