On a crisp fall morning, I showered, brushed my teeth, and sent all that used water down the drain. Half an hour later, I was on the subway, following my wastewater to its next destination: the Newtown Creek Wastewater Treatment Plant in Greenpoint, Brooklyn.

The plant treats wastewater from more than 1 million people on the east side of Manhattan and parts of Brooklyn and Queens. It's the largest of New York City's 14 wastewater facilities, and features pairs of giant silver "digester eggs" that glisten in the sunlight.  

The plant only opens to the public a few times per year — I visited as part of Open House New York, a weekend-long event that grants entry to closed-off sites throughout the city.