Iran’s underground construction beneath Pickaxe Mountain is naturally protected by tons of volcanic rock capable of withstanding anywhere from 21,000 to 43,000 pounds per square-inch of pressure.

As U.S.-Iran attacks continue, Trump says America will hit the underground Natanz-adjacent facility "pretty soon."

"We're going to take out Pickaxe Mountain. Tell the Iranians to be ready," Trump said earlier this month. An expert tells TIME why the underground facility is at the center of…