The Pirran Islands refer to the Isles of Plume, Auron and Keras located in the Pirran Caverns.
After the Shadow Lord invaded the land of Pirra, the Pirrans were forced to use their magic to will the earth to swallow them whole to escape its evil. They settled onto three islands, which they named after the three candidates for Piper that they had tried to back.
Years later, two Deltorans, Alyss and Rosnan, fled into the Pirran Caverns and made their way to the island of Keras, where their children intermarried with the Kerons. Their story was later known as The Girl with the Golden Hair and became one of the Tenna Birdsong Tales.
Later still, the islands were visited by Doran the Dragonlover, who befriended each of the three Pirran tribes and drew a map of the Pirran Sea.
Cavern of The Fear
Jasmine learned about the story of the Pirran Islands when she read The Girl with the Golden Hair in The Deltora Annals. She traveled to the Islands with Glock in order to find a way into the Shadowlands, and was followed by Lief and Barda.