It's a sign that at least some of the ultra-rich are anxious about global events and are making contingency plans for the Big One — whatever form that may take.

The feeling is very much in the air. Architectural Digest named "luxury bunkers" one of the real estate trends of 2023, and a finely appointed redoubt figured prominently in the recent Netflix thriller Leave the World Behind.

Bradley Garrett said the most elaborate bunker he found while researching his book (Bunker: Building for the End Times) is the Survival Condo, located in a former missile silo in Kansas. Built around 2010 by a property developer who used to work for the U.S. Department of Defence, this "nuclear-hardened" structure features walls up to 2¾ metres thick and can house between 36 and 75 people.

In addition to providing each unit with a five-year supply of "freeze-dried and dehydrated survival food," the complex contains an indoor pool, a classroom, a library and two floors of hydroponic gardens to "provide fresh produce." It also has filtered air and water supplies. Units go for between $1.5 million and $3 million.