One day while batman and his sons were out patrolling the streets of Gotham, he got a telepathic message from THE PRESENCE
take his family and build an underground base because there will be a toxic waste spill for 40 days and 40 nights that will kill every impure supervillain in Gotham.
THEPRESENCE told batman he could bring 10 superheroes with him in the bunker
After 2 years the underground bunker inside theBatcave was finally built so batman stocked up on food, water, clothes and morepreparing for the great cleansing.