During the 19th century, the westernmost part of Manhattan at around 35th Street was filled with slaughterhouses. Cattle would be ferried over from New Jersey, and then herded up 12th Avenue (now the West Side Highway) to meet their demise. But as the city’s population grew and car traffic expanded, the cows would cause infuriating traffic jams. The solution: subterranean cow tunnels to shepherd the bovine without interrupting the traffic at the street level. While this sounds amazing, the history of these passages is anything but clear. The podcast 99 Percent Invisible took a deep dive into the history of the tunnels, which is definitely worth a listen. The folklore surrounding the cow tunnels is fraught with inconsistencies—reporters have dug up unconfirmed illustrations of 12th Avenue cow tunnels from the 1870s, and the New York City director of archaeology told a Gizmodo writer that there was no evidence of their existence. But after a whole mess of research, reporters dug up an official blueprint for a “cow pass” dating back to 1932, confirming the existence of a 200-foot-long passage beneath 12th Avenue. The blueprints are dated 60 years after the period when cow tunnels were rumored to have originally been built, but they confirm that at least one existed. The tunnel was likely destroyed in construction during the 20th century, but many claim that it’s still intact. The story of New York’s cow tunnels goes to show that even the people who are most knowledgable about the history of the city’s underground are still unsure of exactly what was—or still is—hidden beneath our feet.