This Vast Photo Archive Is Hidden Inside a Cold, Heavily Guarded Limestone Mine | Atlas Obscura

“But by 2001 the collection could no longer remain in New York. With fluctuating temperatures in a city with four distinct seasons (including hot, humid summers), “the conditions were pretty terrible,” Ahern says. “They had to place this collection somewhere where it’d be preserved, and that place is one-and-a-half hours out of Pittsburgh, 220 feet down a limestone mine.”

A lot of additional details about the collection in this article from 2003