Photo by DMD67.

Among most Washingtonians’ favorite activity is complaining about Metro. Between train delays, single-tracking, overcrowded platforms, and scheduled weekend track work, D.C. residents love to complain about how terrible our subway system is.

But if you take a step back from the everyday adventures of riding Metro, and think about the entire system on a macro scale—a massive system of underground tunnels that connect the entire region—you can’t help but wonder how in the hell did they built it all.

Luckily, Metro just put out this short, vintage documentary explaining exactly how it was done. It is, predictably, quite fascinating. Check it out: