The Eternal Caverns span the whole of the World Below Kayvahn.  There are five different cavern structures in the region including the Oubliette, the Cavirnus Eternal, the Arcanum Antiquas, the Sacro Fonte, and the Obscurite Occulus.  The whole region is known outside of the Hkahnihn Empire as the Eternal Caverns, but within the Empire it is broken into its component parts.  The Great and Holy Ba'alian Empire fills the Eternal Caverns from the southernmost tip of Kayvahn to the northernmost tip.