Blood of Dragons (Rain Wilds Chronicles - Book 4)
Robin Hobb's final book in the Rain Wilds Chronicles finds the dragons and their keepers on a quest to locate the lost city of Kelsingra where they must uncover the mythical silver wells that the dragons need for survival.
Can Tintaglia and the Elderlings unlock the secrets of the ancient city, or are they doomed to extinction?
If you haven't read the rest of the series, here are the first three books:
Dragon Keeper Dragon Haven City of Dragons