Ubar

Ubar is an ancient city buried beneath the Rub' al Khali desert, dating to 7,500 BCE, or 4,000 years before the rise of the first human civilization in Mesopotamia. Built by a non-human species and filled with structures and artifacts best described as strange, including disturbing geometries, proportions, and carvings indicating dimensions beyond. Most importantly, the technology used in this ancient city surpassed any developed by humanity ever since, appearing almost like magic.

The collapse of the civilization that created Ubar was likely a result of a natural disaster, destroying Ubar and other holdings belonging to the civilization. Their descendants would eventually create modern human civilizations, beginning with the basin of the Tigris and Euphrates. The collapse of Ubar would be immortalized as myth and legend, a cautionary tale of a civilization destroyed by its own hubris. It wasn't until Lorenzo Cabot's expedition to the Empty Quarter of the Rub' al Khali that the first archaeological evidence of Ubar and the lost civilization was uncovered and the Atlantis of the Sands was verified to exist.

However, he made only one expedition to the Empty Quarter, and, combined with his famed arrogance and short temper, he was dismissed as a hack.

Appearances
Ubar is mentioned only in Fallout 4.

Behind the scenes
Ubar is a double reference to the legendary lost city in Arabia, also known as Atlantis of the Sands, and H.P. Lovecraft's The Nameless City.