The Soul Reaver 2 Proof of Concept
After the release of the first Soul Reaver, work began on the sequel as another Playstation 1/Dreamcast title. The first known version of Soul Reaver 2 is a prototype running on Playstation 1 hardware built as a proof of concept for the full game. It has never been released to the public, and only a few screenshots are known to exist.
The images of this extremely early version of the game seem to depict a cathedral, and include Raziel using a Glyph spell. It was long suspected that the cathedral was in fact Avernus, the location in Blood Omen from which Kain obtains the Soul Reaver and Wraith Armour. Avernus was featured as a playable area in Defiance, and its altar resembles the one in the Proof of Concept screenshots. It is unknown if this was intentional, but it seems plausible.
It is uncertain if the Proof of Concept contained any other areas besides the cathedral.