* Chronicles of Narnia: This series by C.S. Lewis ends with "The Last Battle", where Aslan returns to Narnia, destroys the false god Tash, and welcomes all the Narnian creatures to his eternal kingdom. The world of Narnia itself is destroyed and absorbed into Aslan's kingdom, representing the end of the physical world and the beginning of eternal life.
* The Chronicles of Prydain: This series by Lloyd Alexander ends with "The High King", where Taran, the protagonist, becomes the High King of Prydain after defeating the evil sorcerer Arawn. This ending is bittersweet, as Taran accepts his responsibility to rule despite the sacrifices made and the loss of loved ones. The fate of Prydain is left open to interpretation, but it suggests a future of peace and prosperity.
* The Chronicles of Thomas Covenant: This series by Stephen R. Donaldson ends with "The Power That Preserves", where the protagonist, Thomas Covenant, finally confronts his past trauma and accepts his destiny as the Keeper of the Earth. The ending is complex and ambiguous, leaving much to the reader's interpretation.
To give you a more specific answer, please clarify which "Chronicles" you are asking about.