Barabus is in the sinister cave, high above the primordial cave; follow the water upstream from the waterfall to get near the entrance.
There are 3 teleporters in Barnabus' cave leading to areas you need to explore. The top one (on a high ledge) leads to a cave with 3 sections (containing the book Igor wants), while the mid level teleporter and ground level one each have a generator that needs to be disabled (to get rid of the shields around the nest and Barnabus).
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