Interested. How about something like uhh

Othertale - The idea that every monster was banished into one single cave system is sorta absurd, surely there are other places where other monsters had been banished to? Join one brave human (or whatever) as they venture into a new world, one unlike the Underground, with it's own set of history, own cast of characters, and own dangerous secrets hidden within

Basically a different cave system with different places, monsters, ideal's, beliefs, and lore. Could be a happier place, could be a bitter sweet place, maybe everyone hates each other, maybe they're super protective? The only thing similar to the original Underground is the barrier that keeps them from leaving.