What remained of humanity after the cataclysm had fled into the caves and underground structures, finding sanctuary there.
For many generations, humanity stayed hidden, unsure what had happened on the surface, and unsure where the gods had gone or if they would come back.
In the caves that had survived the cataclysm, the refugees lived for many generations. They taught their children their ancient histories and mythologies, and passed on what technology they had managed to salvage.
Life was hard and resources few, and over time, knowledge of the past started to fade, technology broke down, and civilisation became more primitive.