The Underground (地下 Chika?) is a subterranean city located beneath the innermost land within Wall Sheena. Many underground cities were founded originally as evacuation shelters for citizens living within the Walls; one was located in Stohess District, but over time fell into ruin and transformed into a pleasure district.
Like many of the other underground cities, the one within Stohess District was originally built as an evacuation site for elite citizens living within the Walls. However, it would fall into ruin over time and was eventually turned into a pleasure district; many members of the elite, as well as interior Military Police soldiers would be frequent visitors to the city.
Along with numerous brothels, the city also became a haven for smugglers, slavers and hired killers. As one member of the Military Police described it, the city is a lawless town where every kind of criminal act that can be thought of takes place. However, some residents in the city simply found it to be a good place to stay hidden from prying eyes. To even get access to the city, visitors must travel down a tunnel within Stohess and then pay a toll that frequently changes.
At some point during the last fifteen years, after the attack by a Titan in Shiganshina District that caused the death of his assistant, famed blacksmith Angel Aaltonen would take up residence within the Underground City. There, he would stay in exile but still occasionally craft weapons for those that would be able to find and pay him. Eventually, a young woman named Sharle would venture into the city in order to track down his location.