What book has giant bats in it that live underground?

It's impossible to give you a definitive answer without more information! There are many books with giant bats, and some even have them living underground.

To help me narrow it down, could you tell me more about the book you're looking for? For example:

* What genre is the book? (Fantasy, horror, sci-fi, etc.)

* What is the overall plot of the book?

* Do you remember any other details about the giant bats or the story? (For example, are they friendly or hostile? What is the setting like?)

Once I have more information, I can give you a more accurate suggestion.