As a NASA science flight was flying over the Greenland ice sheet this spring, a surprise popped up on a specialty radar: a hidden Cold War city more than 100 feet beneath the ice.

As it turns out, this abandoned "secret city" was the site of a secret Cold War project known as Project Iceworm which called for the construction of 2,500 miles (4,023 km) of tunnels that could be used to nuclear intermediate range ballistic missiles (IRBMs) at the Soviet Union.

NASA scientists have located Camp Century, a U.S. military base from the Cold War era, buried deep beneath Greenland’s ice sheet. Built in the 1950s and abandoned in 1967, the base remained hidden under layers of ice for decades.