The Turel encounter was a boss battle planned for inclusion in Legacy of Kain: Soul Reaver. Intended to be the climax of Raziel's excursion into Turel's clan territory level, the boss fight was dropped along with the rest of the level due to timing and budgetary constraints.
The Soul Reaver alphas exposed in 2020 did contain Turel and his territory, although he was only available in one build and he remained static, so the battle could not be truly completed. Parts of his animations remained in the game code and could be accessed through various means. Similarly some of the mechanics of the room were able to be activated allowing for the wall above Turel to break and a waterfall cascade through, flooding the room in the process and this allowed the events of the battle to be pieced together.
When exploring the smokestack, Raziel would stumble upon an audience chamber with benches, overlooking an arena. Raziel walked in but was stopped by Turel, who trapped him in the room. The fight would presumably lead back to the audience chamber where Raziel would bait Turel to charge into the supporting pillars. After all four pillars have been destroyed, the ceiling above them will crack fully and the water from the cistern would pour into the audience chamber, effectively killing Turel and flooding the arena as well. Raziel would then exit the room through the corridor opposite the arena.