Please, read this passage:
Norway plans to build a "doomsday vault" inside a mountain on an Arctic island to hold a seed bank of all known varieties of the world's crops.
What does "doomsday vault" mean ??
Doomsday (the day of doom) is a word used to describe either the end of the world, environmental catastrophe or the end of human life on the planet. A vault is a secure place (in a bank) and the full meaning here is a safe and secure place to keep seeds in the hope that a time will come when they can be used again.