The Raninanis kept hidden undergound. They knew little of the world outside, and that world knew little of their existence.
However, they knew many a thing about the void between dimensions, and how to open gates to it and evoke it in the mind of others. Regularly, they held experiments on creating safe passageways to the void.
But, one time, in the safe abode of their burrows, they opened a gate too big to be controlled. The gate swallowed in the void a major part of the tribe and destroyed many burrows.
This accident was the instigator of a major generational trauma that would run for aeons after the event. They changed nearly their whole way of life afterward. Their homes, usually devoid of superfluous decorations, were now filled as much as possible. The many empty spaces that used to separate their different living spaces were now filled in by walls, who themselves were richly covered.