Buried 600 feet beneath solid granite in Ontario lies a colossal relic of Cold War military engineering — the NORAD North Bay Underground Complex, better known simply as "The Hole." The massive underground fortress was Canada’s front line in the defence of North America at a time when the threat of nuclear war felt imminent. Constructed between 1959 and 1963, the underground complex was part of Canada's commitment to the North American Aerospace Defense Command (NORAD), a joint U.S.-Canadian organization formed in 1958 to protect North American airspace from Soviet attack. The three-storey Main Installation was a figure-eight-shaped building inside a man-made cavern measuring 430 feet long and 54 feet high. With the rise of intercontinental ballistic missile (ICBM) threats and advances in missile detection technology, the air defence role of North Bay's underground facility diminished.