The walled city of Lei Chen within the Lei Chen Mountains.
Lei Chen is a fortified city named after the the Lei Chen Mountains, a mountainous native region of Outworld, that was founded and is currently ruled by Overlord Zeffeero.
Zeffeero once served Shao Kahn for many years, but recently challenged the emperor. Shao Kahn, after years of overtaxing this city's community of all their wealth, sent Mileena and the Tarkatan mutant foot soldiers to retake the city, offering the overlord a choice: deliver his head and have the city's population spared, or have the entire city wiped out.
Shujinko, while exploring the perilous realm of Outworld, delivered this message to him personally from Mileena, but he refused the demand. He then asked Shujinko to get help from the Orderrealm. Without the Outworld Kamidogu, Shujinko offered Hotaru the city itself as payment, which he soon collected. Defeating Mileena's army, Hotaru then relieved Zeffeero of his command and took over the city in the name of Order.
Beyond the city, but still within the Lei Chen Mountains itself lies a tomb-like structure called the Beetle Lair.
In the new timeline, Lei Chin is a high-security prison, which is used for detaining most dangerous criminals, who pose danger to Outworld. Following the events of Mortal Kombat 1, Shang Tsung, Quan Chi, and General Shao were imprisoned there. However, Shang Tsung and Shao's rebels managed to escape after the Lin Kuei broke them out and an afflicted Ermac released Quan Chi, who attacked the construct and fled.