The Abyss

The Abyss was located in the Lake of the Dead. It was the execution ground for "traitors and weaklings" in Kain's empire. The water burned the vampires like strong acid burns humans, so the death caused by this place was slow, torturous and final.

When Raziel presented his newly-grown wings to Kain at the beginning of Soul Reaver, Kain had Raziel thrown into the swirling depths of the Abyss whirlpool, seemingly on a jealous whim. Raziel, understandably, could not comprehend what he had done to deserve his fate. He had served Kain loyally for a millennium.

Somehow Raziel survived. He came to rest at the bottom of the Abyss, and there Raziel encountered the Elder God for the first time. It claimed responsibility for Raziel's continued existence, saying it had spared him from total dissolution. The Elder set Raziel on his quest for vengeance against Kain and his former brethren. Raziel was no longer a vampire, but instead a devourer of souls; a creature of the Spectral Realm that could draw matter to itself in order to manifest in the Material Realm.

Kain did not seem in the least bit surprised when Raziel returned to seek retribution. Defiance revealed that because of Raziel's "remaking" in the Abyss, he was the one creature who actually had free will, and was unbound from the Wheel of Fate. This was Kain's gamble: he hoped that by executing Raziel, he would have a chance to reclaim his destined role as the Scion of Balance. He understood enough about the Ancient Vampires' prophecies to know that Raziel was a key part of this, and his execution was necessary. It was a means to an end.¹

FURTHER OBSERVATIONS

It is interesting to see that the Abyss in Soul Reaver appears to be located directly over where the Lost City was in Blood Omen. Amy Hennig (director and storywriter of Soul Reaver, Soul Reaver 2 and Defiance) has said "there is a connection" between the two², but at the current time, there is no definitive information as to what that link is. As a side note, some people think Vorador's comment to Kain in Blood Omen is relevant. Vorador said "it would be such a pity to lose [Kain] to the Abyss". However, this is inconclusive. As the Abyss, as a physical location, did not exist in Blood Omen, it is just as likely that this was a throwaway metaphor. It could be a fancy way of saying it would be a shame if Kain died.