There's a huge Cold War-era nuclear bunker in Ontario 600 feet underground

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. Built at the height of Cold War tensions, the complex stands as the most ambitious and heavily fortified military project in Canadian history.

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.

Photo: Department of National Defence.

Northern Canada, which was between the Soviet Union and the U.S., was a likely route for Soviet bombers targeting American cities, which made Canada's air defence role particularly crucial.

North Bay was chosen as the site for the complex for a variety of reasons, including the fact that it already hosted an air force base, sat at a key transportation and communications hub, rested on top of billion-year-old granite ideal for blast protection, and had access to fresh water from Trout Lake.

Photo: Civil Defence Museum. 

The complex was carved into solid granite, creating two massive chambers called the Main Installation and the Power Cavern. The three-storey Main Installation was a figure-eight-shaped building inside a man-made cavern measuring 430 feet long and 54 feet high.

The Power Cavern housed life support and utilities and measured over 400 feet long. The facility was designed to withstand a four-megaton nuclear explosion and was protected by three 19-ton blast doors and accessed via two tunnels from the air base and the city.

Photo: Aerospace Defence Museum.

Construction of the complex began in August 1959 and was completed by September 1963. The excavation and construction took four years: 1.5 years to blast the granite and another 2.5 years to build and install the required systems. The project cost approximately $51 million, with Canada funding one-third and the United States two-thirds.

The complex was effectively a self-contained city, capable of supporting 400 people for up to a month in complete isolation. Along with a radar operations and command centre, the facility housed a barbershop, cafeteria, gym, and medical centre. 

At its peak, the installation operated 24/7 with a workforce of approximately 700 people. One of the defining features of the facility was the SAGE (Semi-Automatic Ground Environment) computer system, which was nicknamed "Bonnie and Clyde." The dual computers weighed a combined 275 tons and occupied nearly 19,000 square feet.

Photo: Department of National Defence.

Although the system was revolutionary in the 1960s, it became quickly outdated, and by the early 1980s, it was replaced by the ROCC/SOCC system.

Throughout its 43 years of operation, the facility was continuously staffed, involving about 17,000 Canadian and American personnel over its lifespan. 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.

By the early 2000s, its systems were outdated. In October 2006, NORAD operations moved above ground to the Sgt. David L. Pitcher Building at CFB North Bay.

Photo: Department of National Defence.

Since then, the complex has been largely unused except for occasional storage and, notably, as a film location for the 2013 sci-fi movie The Colony, starring Laurence Fishburne and Bill Paxton.

After 2006, the facility was effectively decommissioned, although some minimal maintenance was required to keep the site from deteriorating. Although the complex no longer serves a military purpose, proposed uses for the now vacant site have included turning it into a home for Canada's audiovisual archive and making it a museum.