If you are looking for a place to wait out the end of the world, why pick a place so affected by climate change (22 square km and highest point is 71m)? Not to mention living off the land is not going to support that many people. This is the entire place: https://commons.wikimedia.org/wiki/File:Aerial_view_of_Nauru...
The other billionaire end of the world bunkers tend to be in more practical areas.
The other billionaire end of the world bunkers tend to be in more practical areas.