If you live in New York City and took the subway recently, or used one of the underwater highway tunnels, or even turned on a faucet, you have a group of men (and a few women) to thank.

Since 1872, Union 147 — or the Sandhogs, as they're popularly known — has worked underground to excavate and construct most subterranean infrastructure projects for the city, clearing and blasting million-year old bedrock and creating tunnels for various uses.

Beginning with the foundations for the Brooklyn Bridge, they have worked on New York's subways and sewers, most of the foundations for the city's other bridges, the tunnels that make Manhattan accessible by car, and the tunnels that carry water into the five boroughs.

These blue-collar workers are truly unsung heroes of the city, mostly because they labor below ground, where their work is hidden from the public eye. Most people never get a chance to see just how hard and important a job "sandhogging" is. Luckily, some Sandhogs have started posting to Instagram, and their photos give us a first-hand look into this relatively unknown, yet essential, craft.