The Descent

So, I just watched this super scary awesome movie "The Descent". Basically this group of women go extreme spelunking down these tunnels and they discover something down there while they can't find themselves back out. So, I was thinking about Dorians idea of a city within a mountain again and thought this could be a great path of discovery. First she finds a mysterious entrance that leads her to a huge cave. She has to then crawl through tight spaces and scoot through tunnels to find clues on where to go next in this labyrinth.
When I was a kid I read this book about these humanesque creatures with glowing green hair that lived in mountain caves. I always loved that story. Here is what these creatures look like. And instead of evil we could make them into good creatures of the dark. Just an idea of a general look and feel of what this part of the game could be.