The Arcis sewers snake underneath the streets of Arcis, and are accessible through manholes.

Within a minute, Zach, Alex, and Ash had removed the metal cover. A dark hole stretched down, leading into the sewers below. A foul stench wafted up toward them, and Alex wrinkled his nose in disgust.... A rusty metal ladder descended into the darkness below, and Ash stepped onto it, staring down at the hole she was entering and desperately wishing she had a flashlight. And a gas mask, maybe. Possibly even a sealed suit to protect her from whatever nastiness lay below.

– Fallen Nation