underbelly
n.the hidden or secret side of a place or situation that is not usually seen. It often describes the dark, dangerous, or illegal parts of a city or a system.
n.the hidden or secret aspects of a place, situation, or organization, typically those that are unpleasant, dangerous, or illegal. Often used metaphorically to describe the less visible, often criminal, side of a metropolis.
“The documentary explores the dark underbelly of the city.”
“While the city's skyline is beautiful, its underbelly includes hidden areas of poverty and crime.”
“The journalist spent months navigating the city's underbelly, documenting the complex networks of corruption that supported the local black market.”
From under- + belly.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.