Deeping Steppes as named by Dargain the Gnomish adventurer who happened upon this place when attempting to find lost friends in a nearby series of caves and was swept in by the unexpected surge of an underground river, perhaps due to shifting of plates or erosion of a natural barrier. The cavern was sealed and unknown until being discovered by Dargain.
This is a region of the underdark where a series of very large plateaus occupy a huge underground cavern. The cavern is situated near a very common and sometimes treacherous underdark route know as The Underway (in my version of the world) which reaches from the Dales to Silverymoon regions in the Forgotten Realms.
The Mad Pope is a wandering mercenary. He is very well deranged as he considers himself to be the pontiff of the dominant faith. His robes are tattered, his mitre has seen better days and there are surely lice in his long ratty beard. What sets him apart from most addle-pated would be holy men is that he has armor under his robes and carries a large crossbow and several one-handed swords. While many would discout him as just another lunatic, for some reason, he inspires others around him and has demonstrated the ability to lay on hands and heal the wounded.