Welcome to Ark Two, the largest nuclear survival shelter in North America. In 1978, Bruce Beach started building the site in Horning’s Mills, Ontario, Canada. An estimated $1 million later — and 42 buried school buses — this 10,000-square-foot bunker could be humanity’s last hope.

Ark Two is equipped with a well for water, toilets, broadcast rooms to communicate with the outside world and enough bunkbeds for 500 people. To get a coveted spot, hundreds of volunteers have traveled here to donate their time and labor. “Without the volunteers, it would be impossible to keep this going,” the octogenarian said.