- "Once a sanctuary against the vampire menace, this abbey has been drowned by the deluge spilling from this wounded land. Your brother Rahab and his brood, devastated even by the feeble rays of Nosgoth’s sun, overcame their vulnerability to water and retreated from the surface. Now they haunt these ruins, and glide in the darkness of its stagnant depths."
- ―The Elder God — Listen (file info)[src]
The Drowned Abbey was Rahab 's clan territory in Legacy of Kain: Soul Reaver. As it's name suggests, it was once an Abbey that had become flooded with water from rain and nearby rivers. The Rahabim, having overcome their vulnerability to water, inhabited these murky waters and the inner chambers of these edifices.
One chamber led, through an underwater tunnel, back to Raziel's territory.
The Drowned Abbey appears to be decorated with sun/moon imagery.
The figures beside the stained-glass windows on the outside of Rahab's chamber appear to depict Turelim, possibly hinting that this was once their territory and they had abandoned it when it became flooded. This may further be supported by the fact that the windows (which were part of the mechanism for killing Rahab), could only be broken with a telekinetic blast - an ability which was naturally unique to Turel's clan as the Rahabim fired bolts of compressed water instead.
In one of the beta versions of the game, a drowned Turelim is seen in one of the chambers. This is further evidence as to the theory that the Drowned abbey was originally Turel's territory and was later taken over by the Rahabim after it was flooded.
Series Artist Daniel Cabuco later elaborated on the background of the Abbey which confirm this:
Look for signs of clans exchanging hands. :)
We left the boat an ambiguous area and hand't really worked out if it was human or Rahabim.
The relationship of the clan leaders was complex, with each vying for favor with Kain, dominance over the others, and using alliances where necessary to strengthen position. Zephon and Rahab could very well have been allies, with Zephon constantly scheming and creating webs of lies, and Rahab seeing through some of it, yet knowing he was better off playing along as an ally until he didn't need Zephon. Remember the bretheren were allies for many many decades, so their relationship was always in flux, ebbing and flowing in power over time. "