The north entrance portal - part of a two-mile long tunnel blasted through solid granite - serves as the primary entrance for the North American Aerospace Defense Command's (NORAD) facility inside the Cheyenne Mountain Air Force Station in Colorado Springs, Colorado, USA, 10 May 2018. The secret government complex is built 2,000 feet beneath the summit of the mountain, in a bunker that can withstand a 30-megaton nuclear bomb, an electromagnetic pulse, and chemical, biological, and radiological attacks