The find was perplexing. In 2015, cave explorers inching through a vertical passage in northern Italy’s Marcel Loubens Cave discovered a partial human skull. The cranium was missing its jawbone, and sat upended on a slim ledge near the top of the shaft. No other human remains were found there, and there was no sign of who might have placed the skull there, or when, or why. Marcel Loubens Cave sits near the center of Dolina dell’Inferno, or Hell’s Sinkhole, a massive karst formation riddled with narrow passages carved into…
