Rotting Cave is a cavern within the Bone Pit. Curiously the cavern has clearly been a shrine of some description at some point, yet remains untouched and unnoticed by the miners. That such an oddity could go so overlooked in the midst of such commotion is almost itself enough to suggest the dark magic has not gone from this place.
It appears during Act 2 for the Forbidden Knowledge quest.
Quests EditForbidden Knowledge
Notable items EditEvil Tome