Surrilana, the vast system of caverns beneath the Himalayas (as described in the pulp serial Morgo the Mighty), is home to a variety of weird creatures. The first such species that McRory and company run into (literally, with their airplane) is the giant manfaced bat. This creature is huge – about the size of a human being, and somewhat intelligent – enough to follow the orders of the masked tyrant Zorimi,
Morgo would make for an interesting RPG setting, something like Savage Worlds.
Someone could have fun with the setting. There’s lots of room to add more creatures and subcaverns.