Rise of the Runelords: Anniversary Edition
Leng is a distant dimension, barely known to even the greatest scholars of the Great Beyond in Golarion. It is an inhospitable realm hedged in by titanic mountains, home to creatures which defy facile categorization or even understanding.
The Plateau of Leng is believed to be either a pocket within the Dimension of Dreams or accessible through it. It is a dry desert littered with ruins. The greatest of these ruins is the abandoned city of Sarkomand, the original home of the denizens of Leng. The most powerful being in Leng, perhaps its ruler, is the mysterious yellow-clad High-Priest Not to be Described, who presides over the plateau’s culture of blood sacrifice. The fabled city of unknown Kadath, while not itself in Leng, can be reached through that dimension.
The primary inhabitants of Leng are the mysterious denizens and fiendish humans who resemble them. Others include the massive Leng spiders, dragonlike monstrosities called shantaks, and the infamous hounds of Tindalos. The runelords of Thassilon were aware of Leng and often conjured its inhabitants to do their bidding; Karzoug the Claimer even built his capital, Xin-Shalast, in a location where the border between Leng and the Material Plane was unusually thin to take advantage of the dimension’s eldritch energies.
Knowledge of Leng is sketchy at best, limited to glimpses in nightmares and drug-fueled visions. Its origin is unknown. Some believe it to exist physically on the Material Plane or another dimension. Others claim it is a surviving piece of a dead plane from before the current multiverse. Yet others believe that Leng is the nightmares of mortal dreamers shaped into a physical place.