In Yevim mythology, Ur is known as the domain of Asag, the Brood Mother, and the antithesis to their goddess, Yevna. It is described as a place of shadow and brimstone, a hellscape crawling with supernatural serpents of Asag's making.
Yevim mythology, of course, tells the story from the perspective of Muraius: that the world was a vast landscape of chaos before Yevna, through Elsene, shaped the land in her image. From the perspective of the Changelings, the world prior to Elsene's reign was a vast jungle paradise, teeming with life. They say even the Northern Wastes were once lush with vegetation.