The so-called 'Celestial Realms' are the unknown region of extradimensional space that exists beyond the confines of the Manifold Sky.
Little is known of the contents or topology of the Celestial Realms other than the fact that it exists on a dimensional axis inaccessible to objects residing within the Manifold. It is believed that some external 'planets' and 'stars' may exist within the Celestial Realms, with a 'sun' and 'moon' orbiting the Manifold (or vice versa) to provide the daylight and 'moonlight' which sustain life within the Manifold.
Fauna & Flora
Life is believed to have originated somewhere beyond the confines of the Manifold, as all sentient species have legends and ancestral memories of the "curved time," where all creatures resided on the surfaces convex, spherical planetoids. At the same time, the presence of life from alternate evolutionary lines from those which created humans (such as the much-feared distal polyps) indicates that life may have been drawn from more than one place at the dawn of history. Some religions, especially the Church of the Unexpected, believe that gods or other intelligent entities might still reside in the Celestial Realms; to date, scant evidence exists to support this claim.