Can anyone help me find a book I read years ago?

I found this book while browsing at the local library years ago and it was amazing! I believe the title was something like Children of Night or Children in the Night. (Not the book by Dan Simmons) and it was about an entire world that was underground. People didn't remember that there was a surface or a sun, but they had adapted for generations to darkness. Cities, caves, and islands in little to no light at all and people relying on sounds to move around. I think there was also a sequel where they found their way to the surface world. The entire storyline was allegorical, good versus evil, love and war, etc. Very mythological, and very intriguing! Please does anyone have any idea who the author is or where I can find this book?