New York City is covered in hundreds of manholes that we pass every day without taking more than a second to think about. While we’ve created a list of the city’s most unique and attractive manholes, it’s easy to literally look past the plainer ones that simply say “N.Y.C. Sewer, Made in India.” However, it’s the second part of the manhole lettering that caught the eye of filmmaker and anthropologist Natasha Raheja, whose new documentary “Cast in India” was recently covered in Gothamist. The journey begins as Raheja ponders where these “iconic and ubiquitous part[s] of New York City’s urban landscape” (as she termed in an interview with National Geographic) actually came from.

Raheja’s exploration took her to Howrah, India, near the Bay of Bengal, where a factory for New York City’s manholes operates. The film, she says, is intended to be more “observational than provocative.” She hopes that viewers will walk away with a better understanding of the workers who create these labor-intensive objects.  She also wants people to think about the mobility of the manholes in contrast to the mobility of the people who create them.

According to The Drive, the process behind creating the manholes involves:

“Blast furnaces are heaped with loads of pig iron carted in baskets on workers’ heads. Armatures that will hold molds in place are picked by hand from rusty scrap heaps. Red-hot molten metal is poured from hand-held buckets, and courses though jerry-rigged brick troughs that resemble hastily built garden borders. Castings are cooled with hand-powered bellows.”

While the workers are unionized, they are paid by the piece, forcing this dangerous mechanism to be completely in a rapid pace. The film also looks at the workers’ struggle to negotiate prices.

For more on the project and film, check out its website here. Next, check out NYC’s unique manhole covers or read about the many, many manhole covers inside Westminster Abbey in London.