-An insane but perspective wizard build it: After a catastrophy, personal or larger in scale, he discovered a fundamental rule of the universe: One out of twenty. One of twenty will suceed in doing the impossible, one out of twenty will fail the easy. Having figured out that Twenty is a magical number, he build a fortress that should chanel energy due to its form, empowering everyone who is in the middle. The euclidian fluids are another part of their research: improbable things, possible consisting out of a material that harvested the power of Twenty, to gain strange properties.
-Or it was build as a monument to a deity with twenty laws/faces which are all of the same importance. To really drive this point home, the building was rolled/rotated everyday, for each facet to be displayed equaly.
-Or it was a simple but well crafted die, that was magical enlarged by a freak accident/a badly worded wish/someone really proud of his lucky die and afterwards people dug in to build homes inside.
-Or insects: they are known to build symmetrical, and in this case some big ones build a strange system.
-Or whoever build it is really obsessed with hierarchy and intelligence, and came up with a complicated system that almost no one can understand(different castes may dwell in different rooms, some obscure laws pertaining room numbers), to satisfy a desire to opress their minions in a lawabiding, intelligence based manner.