The city under the sea that... was a reflection of Amber.
Sometimes referred to as the Ghost City, Rebma is one of two realms that bore a
reflection of the Amber Pattern. The other was the city in the sky, Tir-na Nog'th. Rebma
was forced to become a mirror image of Amber, so that its architecture, landscape, and the
Pattern itself, were reflections of their counterparts in Amber. Following the revelation
that Beatha (Rebma being a simple, insulting nickname given the city) was once the home of
a Pattern in its own right speculation abounds about what 'Rebma'’s true appearance
may be, now that it is out from under the ‘anchor’ of Dworkin’s Primal
Pattern. 
Once located in the great sea off the eastern shore of Amber, the only way for a traveler to reach it safely was by walking down to the bottom of the sea on Faiella-Bionin, the stairway to Rebma. By keeping to the stairway, one could breathe freely and maintain normal body pressure in spite of the watery depths surrounding the traveler. Although gravity along Faiella-bionin was also maintained at Amber normal, if one jumped or fell away from it, one would be instantly crushed by the pressure, even before drowning could occur.
Upon reaching the bottom of the staircase, one walked a direct route toward the elegantly carved arches, approximately two hundred feet farther. One continued walking the ocean floor for a brief span of time until reaching the golden gates of the city. Because of its watery environment, everything in Rebma was covered with a green haze. Tall, fragile buildings formed its skyline, and the palace stood in the center of the city. The palace duplicates the ‘original’, but differed from it in that mirrors were set in its walls, both inside and out.
Corwin's sister Llewella made her home there, and disappeared with Rebma when the Primal Pattern was destroyed. The leader of the city was the Queen Moire, Llewella's half-sister, who put Random under house-arrest when he and Corwin arrived during Corwin’s amnesia.
Years before, Random had lived in Rebma. He had run away with Moire's young daughter, Morganthe, without promising her the permanent bond of marriage. Morganthe returned to her homeland alone, and gave birth to a stillborn child. Months after the failed birth, his distraught mother took her own life.
With Random's return to her city, Moire tempered her desire for vengeance with the calming effect of the distance of years. His punishment was to marry a blind girl, Vialle, and remain in the city for a year's time. Random was still serving his term of imprisonment when the city disappeared, and none know his current condition.