Rub' al Khali

The Rub' al Khali (Arabic: الربع الخالي‎ ar-Rubʿ al-Ḫālī, Empty Quarter) is the largest contiguous sand desert in the world, encompassing most of the southern third of the Arabian Peninsula. It is the cradle of civilization on Earth, containing the ruins of Ubar, an ancient city that predates human civilizations by at least 4,000 years.

Background
As the Rub' al Khali once held the Ubari civilization, it has made locals, such as the Omani, overwhelmingly superstitious of the area. Tales of the area being cursed and forbidden to be in has propagated throughout the surrounding cultures to warn about the eldritch civilization that once existed in the area nearly ten thousand years ago.

Guides were willing to take outsiders, but due to their fear of the area, they were more likely to abandon those who stayed too long in the forbidden areas. This was the case for Lorenzo Cabot and his party in their expedition to find Ubar when they ignored their guide's warnings, who then promptly fled at their first opportunity.

Appearances
The Rub' al Khali is mentioned only in Fallout 4.

Behind the scenes
The Rub' al Khali is based on the real world location of the Rub' al Khali.