Jeremiah suffered a prolonged imprisonment under severe conditions, confined in a highly unusual location. When he was brought to the dungeon, he was not simply placed in a standard holding area. Rather, he was thrown into the absolute worst and most punishing section of the entire prison facility [מצודת דוד, ביאור שטיינזלץ].
The physical layout of this prison is understood in two distinct ways. The primary approach among commentators is that the dungeon was located deep inside a commercial complex. According to this view, a row of actual storefronts selling goods stood at the front of the property, while the prison itself was hidden far behind them. Jeremiah was taken past these active shops and locked away in the inner depths of the compound [רש״י, רד״ק, מצודת דוד ומצודת ציון]. Another perspective suggests that the location had nothing to do with businesses. Instead, the description refers to the structural layout of the prison itself, specifically the separate, individual holding cells that made up the confinement facility [ביאור שטיינזלץ].