Hidden Formation

"Looking at the dense presence of Darkness Profound Energy in this Eternal Night Secret Realm, I would say it belongs to a demon—or at least, a cultivator of the darkness attribute. Furthermore, he would have to be at the Divine King Realm or higher," Aria speculated. 

Divine Cultivators would have successfully formed their inner world at the start of Divine Origin Realm, but only at the Divine King Realm would the inner world become stable enough to sustain life.

"Divine King Realm, huh?" Leon muttered with narrowed eyes before he said, "If the Eternal Night Secret Realm is the inner world of a fallen divine powerhouse at the Divine King Realm or beyond it, then this world could be anywhere."

Just like an interspatial ring that could contain varying sizes of storage space inside depending on its grade, the Eternal Night Secret Realm could appear as a regular pill to the outside yet contain the size of an entire world not inferior to Gaia or greater within.