While flying roughly 150 miles east of northern Greenland’s Pituffik Space Base, the NASA researchers also snapped photos of the polar landscape from the plane’s windows showing a barren, icy expanse. It wasn’t until analyzing the radar images, however, that the team realized what they had flown over without even realizing it.

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.