Yggdrasil, the "Sky Tree", floating in the center of the cosmos. Seen from the front of this skin, it is concealed by clouds, the burning rainbow bridge Bifrost extending towards the viewer.
From the back it becomes clear - It is an enormous ash tree that's used as a meeting place by Norse gods. it rests on a plane containing mountains and all that is earthly. Other worlds unseen are bound by its roots and branches.