The game files for this cave actually contains two caves that aren't connected with each other directly.
They both share one entry in the Glossary, that of the Council Cave, which can be obtained when finding the Krocker Initiation Cave. (Probably a bug.)
This is the place where all the species and creatures on the island met to talk about defeating this large, imminent danger. It's impressive how they found it, locked it off and organized everything inside to include such different kinds.