Very little is known about the shadowy realm of Umbra, save that it is where the Teir'Dal spent years in exile after their escape through an ancient portal during the siege of Bastion (along with the dragon Ithiosar the Black, and that it is home to Innoruuk, the fallen Seraph, who transformed the elves both physically and culturally, darkening their skin and twisting them into the aggresive, imposing and even perhaps sinister warriors that would return to Norrath many years later.
"Though no sun ever rose and never did a single star float in the pitch-black sky above, a strange, faint glow lit this world. It was constant in all directions, but illuminated little, creating a dim bubble of visibility around him. It was as if all of reality had been reduced to a small island that moved with him, floating across an endless ocean of nonexistence. Beyond the reach of the light lay only blackness. Nothing changed as he spent his days searching for the portal spire that had brought him here. For all the months he had roamed, despair was all he found." ~Ithiosar the Black, describing the Umbra
The Sea of Glass - A barren waste of sharp black rocky sand and flat terrain that sustains no life. Ithiosar the Black roamed here for months before discovering Aten, a creature, who led her to the City of Shadows to see the Prince.