- "The west is called 'forbidden' for a reason."
- ―Blameless Marad
The Forbidden West is the Carja name given to the land west of the Daunt. This uncharted region is known for its mystery and danger, as few people who venture there have ever returned in one piece. It is a mentioned-only location in Horizon Zero Dawn and the primary location of Horizon Forbidden West.
Prior to the Faro Plague, the region was considered part of the Western United States: the exact territory spanned from what was then Utah to the Pacific coast. At unknown (and presumably separate) points after the reintroduction of humanity, two human groups, both of whom ultimately descend from the inhabitants of ELEUTHIA-9, found their way into these lands. From these groups would come two tribes, the Utaru and the Tenakth.
Neither the Tenakth nor the Utaru have any form of writing, and so most of the region's history remains unknown. However, it is known that inter-tribal war amongst the Tenakth lasted for generations, while the Utaru maintained a largely peaceful existence.
Iriv, the sixth Sun-King of the Carja, led a total of four expeditions into the Daunt, hoping to break through and explore the land beyond. Eventually he (presumably) succeeded, although he and his army vanished, never to be seen again. To discourage other ventures, Basadid, his brother and successor in the Radiant Line, ordered the construction of the western fort of Sunfall and declared the land beyond it the "Forbidden West," a land where only the Sun may go. This marked the end of the Sundom's expansion.
Over the centuries, many outlanders from the East journeyed into the Forbidden West: most would never return, and many who did were either near-death or driven mad by what they had encountered. Many of these accounts, which were recorded by a Carja named "The Considerate Udain", appear to be largely embellished or altogether fictitious, although there are a few notable exceptions: many explorers encountered the countless ruins of the Old Ones strewn across the lands, and some made it as far as the western coast. One notably consistent part of the varied tales from the West was the presence of new and more dangerous machines, the likes of which have never been seen in the Sundom.
The Red Raids
Jiran, the thirteenth Sun-King, sent Carja troops into the Forbidden West as part of the Red Raids. They faced little resistance in raiding the native Utaru, but the Tenakth of the region banded together and dealt the Carja a crushing defeat.
- "Bold IRIV, who saw the Sun's passing into the West as a challenge, and forged after it with a great army, to be pushed back three times at the great canyons that would be known as the Daunt; until on the fourth time his cohort broke through, and were vanished in the lands beyond;"
- ―The Sun-Kings scanned glyph
- Mathijs de Jonge, the game director of Horizon Forbidden West, has stated that the region spans from what was once Utah to the coast of the Pacific Ocean.
- The Forbidden West's legendary status is similar to the Bermuda Triangle.
- Some of the terrain reportedly found there is possibly consistent with remnants of tactical nuclear detonations from the last stages of Operation: Enduring Victory.
- The Forbidden West bears similarity to the Western Highland from Egyptian mythology, where the land of the dead was thought to be in the west, where the sun set.