The Yin World is the term used by the Shen of the Middle Kingdom to describe the Dark Umbra. It is the land of Negative Chi and located "below" the lands of Flesh. Contrasting to the ferocious vitality of the Yang World, the Yin World is a place of serenity and detachedness.
Like the western Shadowlands, the Yin World is dominated by a Dark Kingdom, in this case the Yellow Springs, which is the dominant power here. While other realms have originally existed, nearly all of them were conquered and enslaved by the forces of Yu Huang. Despite this, places free from his influence continue to exist, like Swar, the Whispering Jungle and the realms of the Tempest.
Among the Shen, the Yin World is the natural home of the Dead, but the Kuei-jin who follow the Song of the Shadow, as well as the Immortal Dynasty of the Xian Lung have the most regular contact with it. Yama Kings whose domains have been reaped from the Yin World include, among others, Mikaboshi and his Wicked City and Wu Hua, the master of the Pit of Salt and Iron. These realms are connected via the Ebon Path, a bridge made out of black ice that is under constant assault from greedy Spectres that seek to snatch away travelers. Some cynics even state that the drakonian rule of Yu Huang qualifies him as a Yama King, making the entirety of the Yellow Springs one of the most successful of the Thousand Hells.