Revelation 6:15-17 NLT
Then everyone — the kings of the earth, the rulers, the generals, the wealthy, the powerful, and every slave and free person — all hid themselves in the caves and among the rocks of the mountains. [16] And they cried to the mountains and the rocks, "Fall on us and hide us from the face of the one who sits on the throne and from the wrath of the Lamb. [17] For the great day of their wrath has come, and who is able to survive?”
In the "Epic of Gilgamesh", ...a few thousand years older than the bible, Gilgamesh saves his people by constructing underground fortresses. Long thought a fable. Recently several have been discovered. Saved from what? The return of The Sun and the wrath/ fire and brimstones, and at times biblical flooding. (yes, water is a solar ejecta) Turns out this star, like many/most, is a transformer...energy to matter... and periodically (like clock work) sheds its outer dense material. It's called a "Micro-Nova". The "Secret of Secrets" is the knowledge of the timing as all surface dwellers are extinguished. Nothing can stop what is coming but those in the know with the financial resources can go underground.
Suspicious 0bservers on youtube goes into the science and context for this, if anyone is interested in learning more.