Planar Travel on a Cuboidal Earth

Once again, I will suggest you read D&D With Porn Stars.  This article is about alternate planar arrangement; specifically, how a cuboid planet would have six different biospheres, one for each face.  This way, traveling to different "planes" involves traveling through the mega-dungeon under the planet.

Since I'm batshit insane, I'm inclined to throw all these ideas together — astute PCs can find alternate planes through dungeoneering, Spelljamming, Planescape-esque cosmologies, or creative navigation through the Mists.  Everything is true!