Wandrils is a system-agnostic random-path inter-planar micro-dungeon (whew!). With a little work on your end it can be easily imported into any game that features inter-planar weirdness (i.e. Troika, Rifts, D&D, etc.).
The space between dimensions is criss-crossed by the wandering tendrils of an inscrutable fungoid entity. Though they cannot rely on the road ahead or behind, gods and fools alike exploit these treacherously unstable pathways to other planes of existence. Littered with planar pests and detritus, the entrances to these Wandrils arise by accident or sorcery - much to the dismay of higher beings charged with insulating the rightful order of the spheres from contamination.