PUEBLO, Colorado—On the dry, windswept plains of southwestern Colorado, a military checkpoint protects a vast field of igloos built with corrugated steel, covered with a thick layer of Earth, and fitted with thick, blast-resistant doors. The walls of the igloos keep the interior a consistent 51 degrees Fahrenheit whether it's in the heat of summer or the depths of winter, and the high-altitude air has little enough water in it that corrosion-causing moisture is an afterthought.
These mounds are carefully spaced to prevent an explosion in one igloo from triggering explosions in neighboring igloos. That's because inside, the US military stores a stockpile of 780,000 unused WWII-era munitions, filled with dangerous and deadly viscous sulfur mustard agent. This stockpile of chemical weapons was shipped to these igloos in the 1950s. They have been carefully guarded since then.
from In southwestern Colorado, robots carefully disarm WWII-era chemical weapons